I think I know what you are going to say, but just in case, here goes.
I need to make a "large run" of mounting plates - for me that means more than five :) These will be 0.065" Al, about 6.5x11 in with four or five sets of related holes. This sounds like a great opportunity to clamp a stack on my mill, with one catch: several of the holes require some counter sinking. The design is more set than it sounds. I have one working prototype, but plan to add some hole sets on the theory that they will end up being useful.
Would you stack, clean up the edges, drill the holes (they need to be reasonably precise, at least relatively in the different groups), and then separately do the counter sinking on a drill press? Next up would to be position stops to allow me to individually re-clamp the plates to sink each plate on the mill. The only other alterative that I see is to make the plates separately; I enjoy milling, but have better things to do, unless that is really the only viable choice.
If you get serious about making parts, one of the investments you should make is a micro-stop for countersinks. They control size very well, and don't need precision locating, due to the use of a pilot. They can be used in an inexpensive drill press with excellent results. You can stack drill your parts, then go back with a second operation and do the countersinks.
You can do the same thing by establishing some simple stops on your mill table, then countersink the same holes in each plate by going to proper location. You need not clamp the parts, just bank them well against the two stops. This setup requires that your parts are all drilled accurately from common datum points----so try to make your plates identical in size, and insure that they all locate properly when you make your setup. By countersinking this way, you can set a spindle stop to control the diameter (or depth) or the countersink.
Regards part size, I've always made it a practice to hold dimensions closely, and the parts square. That way you can bank from opposite edges when necessary, and still hold tight tolerances in hole spacing when all the holes aren't drilled in the same setup. .
Here is a quick way. Mill a template out of Plexiglas, about 1/2 inch thick. blank out your aluminum sheets a little larger than your finished size.
Attach a sheet of aluminum to the Plexiglas with some double stick masking tape and using a flush trim router bit cut the blank to finished size. Now before dismounting the sheet drill your holes. Now all you said was that the run was more than 5, but let's say that it is 20. With only 20, if you were to have your holes drilled in the Plexiglas you could use those holes to guide a drill bit before they degraded beyond tolerance.
If you had to do more than 20 you could use the holes in the Plexiglas to guide a transfer punch. Alternatively you could set drill guide bushings in the Plexiglas.
On countersinking, the counter sink will allow the plate to self center so setting the depth on the drill press you can knock these out quick.
You should be able to hold +- .003 with no problem.
That sounds useful, all the more so because I have a Ryobi drill press that has been largely collecting dust since my mill arrived.
I follow most of that. What do the stops look like, and how do you ensure the part aligns with the axes of the mill?
I suppose one could mill the plates and use them, still clamped in place, as stops to position the stops; if that works it would keep the numbers from the milling of the plates. It seems safer to make the plates, remove them, position (probably indicate??) stops, and then find edges/zero based on a square or a squared plate clamped against the stops.
What am I missing?
The more I follow that advice, the more I agree with it. With a stop at the correct height, it can be very helpful in milling things that need to be approached from multiple sides. I took advantage of it just today to alter a part that holds something that a manufacturer changed "without notice". I was able to seat the affected part on parallels, find its left edge (the transverse dial was already zeroed on the on the back jaw), and put an additional hole in it to accomdate their design change - fit like a glove :)
Thanks for your substantial role in teaching me how to do this stuff.
Not really, though it certainly would work. In terms of my time and given the small number of parts needed, it would be quicker to just mill them, and I need the practice anyway. If I were making many (by real-world standards) of them, then it would be a natural choice.
There's a couple ways you can go about this setup. One, you can use a couple of parallels that are the same thickness as the slots in your mill table. The slots are usually fairly close to size, and will have a minor burr on the bottom corner that will hold the parallels in place when you tap them in with a soft hammer. Use two of them spaced such that your part is located on each corner. For the third stop, the side, use something that doesn't present a large area, and make it anywhere from the center of the part to the bottom edge. When you bank your pats, they should bank along the two parallels, which should establish the part dead parallel with the table, and the side stop will locate the parts consistently with one another. Once you've made the setup, use an edge finder to orient the spindle with the part edges, and mark the table and saddle according, plus set your dials. If you use a DRO, you'd zero it according to how you'd work. Once you've made this setup, you should be able to remove and replace each part reliably. It's a good idea to not have any chip traps where your parts locate. It's also a good idea to work with edges that have been deburred, so nothing will prevent your parts from locating against the stops.
If you follow the procedure I outlined you should have good luck. Let me know if you're either confused, or find something I left out. I've used this procedure for years with good luck.
I think I get it now. An alternative would be to make a fence that can be indicated parallel to the table and then use a round side stop. Is that reasonable? If I understand about the parallels, I don't have anything that thick (though perhaps I should), but I do have a few candidates for a fence. One tricky part is that the plates are designed with my cross travel limits in mind, so there isn't much wiggle room. However, the fence could be an L section that is bolted underneath the top edge of the plate.
Understood re the edge finder and dials. I do not have a DRO, and am really not burning to get one. If I can get a scale to sit flat on a part (clamps sometimes get in the way) or can at least reach an edge and a point of interest with a dial caliper, then all I seem to need is a course (+/- 0.1 to get the correct revolution) after which the dial takes over. I have not yet zeroed based on an internal hole; that might get me to change my tune, but for now, I'd rather keep the cost of the DRO toward other things.
Yes, it is---the one advantage of using parallels is that you eliminate a large area of contact. That's a good thing. It's too easy to get a chip or other bit of crud between your part and fence, but if you use good work practice (and an air hose), plus deburr your parts before you start the second operation, it shouldn't be much of an issue. I'm not sure I was clear on the "chip trap" I spoke of, but that's what I meant. You have to be alert to not get things between the part and the stops.
If I understand about the parallels, I don't have
The L section would work entirely, assuming you didn't try to use both full length edges. It's fairly important that you don't do that. Parts, or stops, are rarely perfect. You want your parts to locate the same way each time, thus the small side stop and double stop at the top. Or, you could reverse it, just make sure you use three point stops, and always bank against the two to square the part. If you use the L configuration, relieving the short edge might be a good idea, or you could just make it very short. The corner should be relieved, too, so it doesn't interfere with locating.
That's a tough way to learn to drill, but once mastered, you don't really need a DRO unless the screws aren't worth a damn. I've always taken great pride in working without one------and did work that was subject to tight scrutiny (defense work). I comment you for learning the system----you can always use the cheat devices, but if you lack the fundamentals, you'll always struggle with these things. Learning to use the screws is the core of all the work.
I have not yet zeroed based on an internal hole; that might
Only if your holes relate to one another would I suggest that. As long as you use the edges as a datum point, you can check your movements with a scale---which will pick up even small mistakes (transposing numbers, for example) if you pay attention. It works very well for picking up an added turn of the dial, or one that has been dropped. That is also one of the things you must master when you work by this method. Keep your scale handy at all times. I never run a machine without one within arms reach.
There may be times when you must work from a hole. When that occurs, make the hole the 0-0 point, then you can crank off directly. Checking with a scale or caliper isn't all that hard, especially if the hole is a fractional size, such as 1/8"----you just measure to the edge and add the radius. Easy enough, and can be done in your head.
Then I probably do have parallels that would fit, but might not trust them to stay put or to align all that well. I would also have trouble clearing them, at least with the parallels I have now (6 inch length). It does give two nice points of contact, and a round stop at the side would do the rest.
Either way, this suggests a simple change to the fence idea, something like this:
+----------------------------------------------------+ | |
+--------\ /----------------------------\ /----------+ | - - | | | | O O | | |
One would drill holes, bolt a plate to the table, and mill the fence with a couple of bumps that become the stops. Then indicate off of the fence to align it for use. In fact, with a large enough plate, one could put the side stop on the plate, though that is probably not necessary or even a good idea.
There might be better ways to make it. It would be easiest to do with Al, but that might not be a good choice for something that takes any kind of pounding. I probably could make it from steel, but it would be painful. Is there a reliable way to combine a couple of sections that might simply need to be faced vs. carving an L out of large plate? It wouldn't be much good if the pieces slipped.
Mine appear to be in good shape. In fairness, most of the work I do is making parts that align with other parts made on my mill, so I could be missing some errors. However, I have matched holes from the outside w/o problems. Well, there was the one time that a major manufacturer's drawing was in error on one hole ;)
It's really not that hard. I made a simple spreadsheet to help with windows; given the desired edge locations, it handles the tool radius and leaving some extra metal.
One thing that still bugs me a little is finding the reverse-direction dial reading. I pretty much know the amount of backlash, but still suspect I should do it by feel. What I do is move forward to the desired reading, then back up until "the screw hits" and note the reading. Then I go forward again, trying to get the same reading as before (again w/o moving anything). If it doesn't work, I alter the reverse direction reading and repeat it. I usually get it on the first or second try. Please let me know if there is a better way.
I bought a scale as soon as you first suggested it to me, and immediately saw the value of it. Do you do anything special to position the scale at the edge of the part? I tend to use my finger as a stop for it, but there is probably a better way.
Another trick would be to put relevant distances on the drawing. I am shameless about over dimensioning when it helps. There is a tradeoff between having the needed distances in view and having so damn many of then that it's easy to read the wrong one, so some discretion is required. Certainly a reference to edge distance belongs on a shamelessly dimensioned drawing :)
For anything that gets difficult to read, I frequently use multiple dimension layers, and print the drawing one time for each layer. One of my uglier examples is a plate with 11 slots, 3 windows and 40 holes; I used three separate dimension layers. More frequently, I use a layer for milling and another for drilling, and for really simple stuff, I create just one dim layer.
Back to holes as reference, my primary interest in the idea comes from using internal holes for clamping. For my upcoming stacked plates, I can simply add holes and not worry much about their location; they need to be reasonably close transversely (to align with the slots) and not hit any "working" holes - there is plenty of room. However, not all parts can be punctured at will. Perhaps the answer is to still reference the edges, but not bother milling all the way around at first, so there would be little if any reason to move clamps. With a clean left and back edge, the references are set; then one could position internal holes with precision. If there happens to be a t-slot under a few of the holes (courtesy of a favorable transverse location on the table), they could then be used for clamping, after which the external clamps could be removed.
Only work from one side of the screw. Let's say you have zeroed the dial turning the crank clockwise. If you need to work backwards from that point turn counter clockwise to beyond where your desired point is and then come back turning the crank clockwise. This doesn't account for wear in the screw itself, but usually the wear is in the brass half nuts so this is usually not an issue.
If you are milling a pocket, you of course can't over shoot without taking the cutter out of the work.
Taking the time to square your stops with an indicator and making sure everything is good and snug is good practice that leads to precision results.
Another thing that helps avoid the brain fart errors is to layout the part with scribe lines and that way you can see if you have not counted your crank turns real easy.
Take a piece of angle iron. Drill two hole in it to receive short carriage bolts. Nut on each side of one leg of the angle iron. Tighten the bolts up evenly. Place your raw part on table, bring bolt heads up to touch edge of plate. clamp othe leg of angle iron down without moving. Every new piece you put in there will only touch those two points of the rounded bolt heads.
That's correct. Years ago, when I was in training, we had pretty much full shop capabilities, at least within reason. While I never ended up with a set, the journeymen made small sets of locating jaws, more or less short parallels, but stepped. They were heat treated and ground. They could be used for two different T slot sizes, and stood above the table a small amount, maybe 3/4".
Yep! I agree. They do get in the way, depeding on the job at hand. You might find you can use parallels installed the short way. You can use only a short portion of each one, with the balance beyond each end of the parts. Reason? If you have a minor deviation in either of them, it can't be much, due to the slot size. By spacing them, neither of them can steer the part----and you'll have minimized the inherent error, should you have any.
As I said before, because T nuts tend to swage the T slot tight, if you make them nominal slot size, they are a light tap fit with a soft hammer. Not deadly accurate, but when you use a pair of them, you can expect alignment within a thou----which is pretty decent if you space them as far apart as is possible. Typical shop tolerance is .001"/inch, so you'd be well within tolerance on all but the most demanding of jobs. When it must be closer, you, of course, resort to a DTI.
Make your plate of aluminum, and thick enough, so it becomes a great work platform for multiple jobs. If it's thick enough, you can drill into it for through holes as an added benefit.
I tend to work off parallels all the time, to avoid every touching the table. My mill was purchased new in '77 and has no pecker tracks on the table.
Regards the third stop, the side one----it does no harm to not have it on the base plate-----that way you won't be limited to the size the plate can accommodate. You may find yourself working with a long plate with a hole pattern in the center. You can set a stop real easy by using a hold down bolt and a few thick washers, and place it accordingly. All you really need is an elevated platform that is straight cut, but if you do lots of small stuff the L shape could prove pretty useful----with a stop on the left side included.
Regards milling the L shape----no real need. Use a thick plate, then drill and ream for dowel pins. Do all this after milling an edge, so you have a reference point for setup. Dial in the machined edge and your dowels are parallel to table travel. Dowel pins are heat treated and ground, and cheap! Again, you can even use one for the side stop. They present almost no surface area for chips to prevent proper banking.
For starters, the only way you can reliably work with the screw in both directions is to measure. Even when you know the amount of backlash you have, there's no guarantee it's uniform. Backlash occurs because of wear, which we all know. Thing is, the wear doesn't occur strictly on the nut. As a machine ages, the screw will develop wear, too, so the amount of lash you have will be different, depending on location. Probably not a serious problem, but it can be if you have a narrow tolerance. I make simple pencil sketch on a piece of paper and trust the dials in the two directions that are proper, then cut and measure when I reverse the screw----marking the dial, or recording the reading for finish size on all edges. The sketch I mentioned consists of a cross, with the appropriate dial reading at the end of each of the arms. I do all my finish cuts by climb milling, and backing off the corners about the amount of the backlash as I enter them. You can cut windows without a trace of undercut that way. The little sketch will keep you out of trouble when you have more than one part to do.
I use a finger or thumb nail, but if in doubt, I'll often use anything rigid. A small parallel, or even another scale. You'll be pleasantly surprised to find you can see as little as .003" error, although not reliably.
I didn't have the luxury of generating my own drawings, I sub-contracted from outside sources. That didn't prevent me from re-dimensioning prints with a pencil, however. I did that routinely. Unless the draftsman has worked on the machines, and works the same you do, he's not likely to present information in a useful way. I've rarely found prints dimensioned such that you can build parts without penciling in dimensions that are functional for the guy twisting the handles. . Often I'll re-dimension from a different edge, but I work such that it changes nothing, it just allows me to read my dials in the same direction all the time. I avoid reading them backwards if possible. It's all in the work habits you form.
By the way, from what I'm reading, you have really taken to this stuff. You don't really need much help---your thinking is quite good.
Heh! Where I came from, anything that wasn't on the print equated to making scrap. You learned to make setups that didn't harm parts in any way, including clamping marks. The idea of drilling holes for manufacturing purposes wasn't a consideration, but if you can do that and not create problems, go for it.
Perhaps the answer is to still
My procedure rarely provided for partial milling, then drilling and final milling---but that doesn't mean it isn't a good idea. One part I made had such a tight tolerance that I actually did work from a hole, using a pin. All dimensions were generated from the hole as the part progressed. 26 operations in all-------and when the job was finished, all 209 of them fit in the palm of one hand.
Circumstances can dictate what works best-----and often do. Regards plates, my personal method was to always take them to final size----again, if for no other reason, I may need the opposite edge as a datum point. I not only took parts to size, but I held them close-----a target of /- .001" always. I still have one that I made for Univac, years ago. It's a chassis made from 1/4" thick aluminum with holes drilled and tapped in various locations, plus counterbores for transistors. I mention this part because it's a classic example of having to turn parts over and pick up existing work for a second operation, which justified holding lengths and widths close. Tough job, all done without the use of a DRO. If you're curios about these parts (the tiny one, quantity of 209, or the chassis), I can send a pic by email if you're interested.
If you work as I did, you'll get more than a few arguments from young machinists that are production oriented, at the expense of quality and personal satisfaction, but the most successful machinists I used to know all worked that way----and acquired the respect and acknowledgement of their peers. That's how it was before CNC---at least in the defense industry I served.
Sounds good. I think for the stacked plates, I will start with the assumption that the sinking can be done on a drill press. They do not need to be pretty, just enough to "hide" the machine screw heads without being too deep as to weaken the connection.
No troubles so far.
I guess my question is really how to know where to take the first cut. I typically start a window by locating the (inset 0.010" or so) corners, plunging about 0.020" (in truth, I stop when I think it's enough to see it later). All four corners can be marked by moving with the dials, but eventually I have to start moving against the dials, and I find it helpful to have located the reverse dial reading by my feel/check method. When cutting the window, the holes at the corners allow me to see when I am on the last revolution, after which I look at the dial; if I have a good guess at the backlash, I usually don't get into too much trouble.
Ideally, one would expect to find 0.010" (or whatever was left for cleanup) all around. I usually find that the reverse directions require different corrections. I think that is what you are saying should happen, but let me know if I'm in error.
Do you mean something like below?
34 | 22 --+-- 75 | 50
I'll have to try it to be certain, but that looks it would be very helpful and simpler than my drawings. I have been drawing a window and placing the numbers around the box. I do no always use my spreadsheet, but it adds absolute locations; they could always be written under the dial readings on your diagram.
That's high praise from a respected source. However, my thinking is good enough to know that I need a LOT of help :)
Any advice for avoiding marks?
For the plates in question, a couple extra holes won't hurt anything. BTW, said holes _are_ on the print ;) I design with my shop in mind, and in this case, I am pushing my mill nearly to its cross travel limits, making the internal holes an attractive idea.
That reminds me that I would like to get your thoughts on my 8-24 Cross travel thread. I am in no hurry to buy a new machine, but I want to have thought about it in case a used one appears [*]. I also want to form some guidelines for what I would buy if I were to buy new. The conscensous here seems to be that old American beats new Chinese. I have no problem with that (I drive a 16 year old car by choice), but wonder whether I would be happy with a heavily worn machine.
[*] If you have not done so, I highly recommend reading "Failure is not an Option" by Gene Kranz.
Does that mean a reamed hole and indicating on the outside of a pin inserted into it?
I can see the time=money argument agaist it, but I completely agree with you any time something needs to be approached from different directions. For now, I try to hold close tolerances on everything just to get the practice.
I am indeed interested. Please feel free to send the pictures.
The good news is that there is nobody around to argue with me - the bad news is there is nobody around to help with the work. While not true globally, I am pretty much a corporation of one with respect to machining.
Yep! Exactly. The two dial settings come directly from the dial (with the dial, which in almost all cases, is RH rotation for me), allowing for cutter size, naturally. The other two come from measuring from a datum point. It can be the opposite side of the window, just as long as you know where it is. I often take the window to size, minus five thou on each side, then use that surface for measurements to establish final marks.
Problem with a spread sheet is it assumes some things-----this method works perfectly because you cut to known stops, determined by measurements. All depends on the job, and the tolerance at your disposal. Nothing wrong with what you're doing if you find it works for you, and you're making good parts. When the work is critical, all four sides should be measured to establish the stop points, the dial, nor a spread sheet, should not be trusted. I'd say for anything with less than .005" tolerance. I would never trust a schedule for tight tolerance. It has a way of biting you on the ass.
It's a good idea to keep a small amount of 1/8" soft aluminum around--kept clean, naturally. A small piece under the clamp works great. If a job is really critical, paper under the aluminum shim is also useful. You can usually handle parts without a sign if you use your head. One of the problems with a mill is denting the parts when your clamp is low at the heel. I make it a policy to have the heel slightly higher at all times, then use a soft shim under the point of the clamp. Parallel clamping is also a good method because it spreads the load over a large area, but I've found I often damaged parts that way due to minor irregularities. Best to use clean shims, at least in my opinion.
That's the best of all worlds. Holding work can be challenging. When you run a lathe, I can't think of anything that serves you better than soft jaws.
I'll give you something to ponder----but I don't think I should be making decisions for you. I don't have a problem speaking my mind, for me, however.
Machine tools cost a lot of money because we pay for precision. Iron in and of itself isn't very desirable, I'm sure you'd agree. I've heard all the arguments about buying old American iron, but, frankly, I just don't agree. I've run enough machines to know that when the useful life is gone, it doesn't matter how good it once was, or how great the builder's reputation may be, or have been. What really matters is can the machine serve your needs? My money says an old worn out American machine has another name----and it's sure to anger some guys. SCRAP. Just because a machine can move metal doesn't mean it's a good machine.
I won't ever forget running an old #4 K&T horizontal, which had the vertical head accessory. I was trained at Sperry Utah Engineering Laboratories, in the late 50's. They were under contract to build the Sergeant guided missile, so they could acquire used government machine tools for the shop. One of them was the K&T I speak of. I was cutting some slots in a length of stainless angle, a corner for a cabinet, and trusting the dial (big mistake). I had little experience on machines at this point, but I was giving it all I had. When time came to inspect my work, nothing was as it should have been. The screw on that mill was so badly worn that it was gaining or losing no less than .015" in a few inches. The machine had obviously seen a lot of action during WW II. Could a new import machine be any worse?
I don't do a lot of reading, mostly because I don't have a lot of spare time. I read the paper daily, and the Smithsonian magazine-----then things that interest me. I'd like to explore your recommendation, but I'd appreciate a clue regards the contents of the book. The title is intriguing, at least to me. It very much describes my attitude about the things I do on a daily basis. I ran my shop that way, and the precious metal refining business that replaced it as well. I've always done things the very best way I could--and don't have a lot of patience for folks that gloss over everything.
By now, you should have received the picture I spoke of. The pin was a part of the holding fixture---simply---a drill blank. The parts were too small to handle by most any other method, so I made what was soft jaws for the mill vise, then milled the jaw away as the part took shape, leaving only the profile of the part intact. The pin was in the jaw, and located the part for all dimensions. It was one of the first features on the part, once the blanks were squared. I trusted my dials for dimensions once they were properly marked in relation to the locating pin Holding the parts in a vise was a serious challenge. Tighten it too tight and you lost location----and crushed the parts. I ended up using a small parallel clamp (1-1/2") as the vise handle. Worked great. Used the same two fingers to tighten the vise each time for consistency. Sometimes you have to think out of the box.
I highly commend you for that. If you learn to work closely, in the end it takes almost no more time, and you save what little you may spend by not having to screw around with the parts for succeeding operations. Pay attention to "hackers", guys that think that you need not work closely, except on rare occasions. These guys never master the art of close work, so when it comes along, they can't do it worth a damn. Fine work is different from hack stuff----and you must know how to do it if you want to succeed. You can't do it occasionally and ever get there. It must become a way of life. Many don't have the balls for it-------and many don't care, even if they do. I'm not one of them.
But------you have at your disposal some good people to provide guidance, and it's only a few clicks away. The only problem I can see is it's hard to separate those that "can" from those that *think* they can----but it slowly comes out if you read long enough. There's NO substitute for experience when it comes to running machines. You can have all the knowledge in the world in your head, but if it doesn't come out of your hands, it doesn't matter. When you watch people that know what they're doing, they look different. I mentioned this recently---hope I'm not repeating myself here. It's not so much what a guy or gal does that knows the ropes----it's how they go about doing it. That comes from experience.
Let's see if I follow. You are saying that you take the desired location of the cut, back off a measured cutter radius plus five thou, and use that dial reading. That is what I do, except I leave ten thou, and I generally don't measure the cutter, except to check new ones to ensure they won't double cross me (if they are over sized, I clearly want to know). If I had more faith in my ability to measure from edge to edge, I would probably take the time. Any tricks of the trade for that measurement?
Are you saying that you turn the dial backwards until the edge of the cutter is where you want it by measurement? What do you use to make the measurement?
I have always made a cut that I have good reason to think leaves some excess metal, and measure the part (with a dial caliper) to find corrections.
Agreed. The spreadsheet always spits out numbers that leave some metal (ten thou by default), after which I measure and alter the readings. I end up crossing out numbers writing new reading beside them.
Sounds good. Is there any concern about the shims helping the part to slip?
You won't be making decisions, but I do value your opinion. If I buy something too big or too small, that's my problem, not yours, so I have to make the decisions. There are no immediate plans to buy.
INTERESTING. My opinion on this has been swinging from the ultimate being a used/rebuilt BP to preferring a new machine that a future version of me inspected, trammed, etc. prior to purchase. This is based in part on posts such as "yeah, the screws are shot, but with a DRO who cares?" and my experience with my own mill, which is a hell of a good machine. If I ever reach the point of going out of my way to buy a knee mill, a six hour drive to Atlanta or other hub location would not be out of the question.
That machine probably saw more use in a few years than I could realistically give a machine in decades of prototyping and tinkering. Perhaps all the more reason to buy new.
Again, I am not in a hurry. The BP, owned by a little old lady who used it only to square a block once a year, has not appeared, and I am not at all certain what I would buy. If I were willing to kick my car out of my garage, I could get a 10x54 with no space worries. But, the car deserves better. An 8x36 seems a bit small cross travel wise (not much of a jump over what I have now), and a 9x42 is a big jump in weight. Benchtop knees are nice enough, but the travels are typcially worse than what I have now. So far, I'm hindered more by travel than by mill-drill setup snags.
Gene Kranz is a living legend. He began as a military jet jock and then joined NASA fairly early in the space program, becoming a flight director. The book is littered with history of Mercury, Gemini and Apollo.
If the insights into NASA don't interest you, the insights into Gene Kranz will. Get a paperback copy and a bookmark; you won't regret it.
I haven't seen it. Sometimes that is my fault. Spam dominates my incoming mail (as it does for most people), and I know I occaisionally delete things in error. Our server will bounce some messages, such as those with a .zip attachment (but you can rename a zip file to have .z extension and it will come though - the system will even offer to uncompress it!!!).
I apologize for any inconvenience. A good starting point would be to send a quick test message to make sure we are using the correct accounts, and can coordinate it further offline. I would very much like to see the photos. Also, I just sent a message to the address that appears to be yours; you can simply reply if you see it, and we can work up from there.
Considering I used to have my end mills re-ground, measuring them was always important. Further, new end mills tend to not run true to size. On many occasions I found four flute end mills to run slightly oversized, but two flute on size, usually within a half thou. When working to a tight tolerance, it can spell the difference between success and failure.
It shouldn't really be much of a challenge, considering most cutting tools have opposing faces. Not true in all cases, naturally---such as a three flute end mill.
It requires a light touch, and I highly recommend carbide faces for the micrometer. It is also a good practice to measure the portion that you actually use, not well up the cutter. That may not matter with end mills unless the end is badly worn, but drills are not straight. Particularly when measuring number drills, where size from one to the preceding drill may be only a thou different, measuring near the shank will provide a useless measurement. It helps to look at the tool as you measure----I simply spin the tool slightly as I bring the spindle against the lip--and stop turning the spindle when I feel contact. A little fussing tells you when you're in proper contact. You should be able to measure drills or end mills within a couple tenths----far more precisely than you can work manually.
If you've read my posted ravings, you'll know that I am NOT a fan of calipers. They lie to you way too much to be reliable. That's not to say I don't use them---I do---but I try to never trust the readings----and I'm usually well rewarded for not having done so. I use micrometers----relying on calipers only when nothing else will work. If you have a broad tolerance and don't care if you miss dimensions by a few thou, hey, no problem. Frankly, I'd trust my ability to measure with a scale before I'd trust calipers. I've consistently measured the lengths of shoulders within .003" with a decent scale-----although I will admit that was when I was young and had good vision. I doubt I could do it today.
Cool! A man after my own heart. A perfectionist. Based on that, your spreadsheet is a great idea. It's always nice to have something that gets you close, so you don't spend unwarranted time getting there. The time spent making corrections for the actual location is what makes the difference, and I commend you for your technique.
The available tonnage appears to be the ruling factor. As long as you use more than one clamp, slipping has never been a problem for me-----and I am not a ham fisted operator. Having run grinding machines for a few years, you learn to tighten bolts adequately, without over-tightening. That's important if you expect good performance from a grinder. Placement of the hold down bolt as it relates to the stand-off makes a huge difference, too. By keeping the bolt near the part, away from the stand-off, you apply the vast majority of pressure on the part----where it's needed.
That's a good thing. Keep your eyes open----and don't discount the clones of BP mills. Some of them are huge improvements over the BP----more robust, with heat treated ways.
I've owned two BP mills, both purchased new. I have no problem speaking the truth, some of which isn't complimentary. I made the choice for one reason, maybe two. One was the incredible flexibility. They offer easy operation---and a head that can be tilted or rotated anywhere you desire. The turret on a BP is one of the features that endears the machine to use. You can work off the side, with long objects, or swivel the head to continue a cut without resetting your work. Still, they are far from a great machine, and are highly over rated. Were it not for the price (the other reason I bought), which at one time was very reasonable, they wouldn't have achieved the status they enjoyed. I've operated mills that make them look bad-----Gorton, for one. Problem is, unless you buy the BP pattern, none of them offer much flexibility. A Gorton 9-J, for example, is ten times the machine, but you can't move the head in any direction. Great machine, but only for straight away milling and drilling. No trick stuff.
If the screws are worn to the point where it's a problem, why would anyone expect the balance of the machine to be any better? Slides wear away, too. The issues with a badly worn machine are a serious consideration-----and can't be solved without spending huge amounts of money--even when you do the "restoration" yourself, assuming you want to dedicate the time. Nothing wrong with doing it----I recall with great pleasure an old 8-D Gorton that was nothing short of an anchor----that was fully rebuilt by one of our machine tool repairmen at Sperry. New screws and nuts, and all surfaces re-scraped, including the knee ways and table surface. When it was finished, it was the nicest machine in the shop. BUT-----it took time------lots of it. Having worked as a machinist and toolmaker, not a machine repairman, I'm not sure I want to spend my time making a machine work----that's not what I did, nor what I desire to do. From the sound of things, you are involved in a project of sorts----and maybe should not be dedicating your time to making a machine perform properly. Rebuilding a machine probably isn't a good idea---but I may be wrong. A new Jet mill surely would serve one better than a clapped out BP.
My first BP had the 36" table. Big mistake. I needed the extra travel on many occasions. I agree---buy the largest machine you can accommodate, keeping within the drop spindle design. Again, it all depends on the work you do. That old 8-D Gorton I spoke of was a wonderful machine, but very limited due to size. I made a nice 8 cavity 9/32" lead ball mold on it, trusting the screws. Turned out beautifully---but the machine was limited to small stuff. Not a solution if you do large work.
Thanks. There's a used book store in the "big city". . I'll check it out the next time we go there. We live out in the country---nothing available for miles.
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