I believe I am ready to take the plunge and replace my mill/drill with a real milling machine. Later add a drill press (or sooner if I can find good used), hence my previous post on drill presses. I don't have space to keep the mill/drill as a drilling only machine. Little brother has his eye on it anyway.
So now for the really stupid question. I have the option of getting a DRO with the mill. I've never used one, so I don't know what they are like. This is the first research I've done on them. They almost seem like they can be used as a manual CNC. I'd also guess that if you are just drilling a hole you wouldn't have to worry about backlash as the measurements aren't taken off the leadscrews. So is a DRO worth it or is it just a fancy gizmo that really isn't necessary?
Get the DRO's. My mill didn't have them when I bought it used, so I ran for a year or so just remembering to take the slack out in the same direction every time etc.
Had a job come in that was a pair of blocks, one mounting 40 .750 punches, and the mating die block with 40 dies. Punch to die clearance was .001. Bought DRO's, installed, machined blocks. Put them in press--pushed button. 40 punches into 40 dies, no crash. WooHoo!!
I do a lot of bolt circles and holes located x-y. DRO's are money well spent.
No, you don't need one. Machinists got along for a lot of years without DROs. It's just that you'll find yourself spending a couple hours doing what you could have done in ten minutes, if you had the DRO... (sarcasm mode off...)
What really pays off is if you also have a good CAD program on your computer. That way, you can draw all sorts of complex stuff and turn it into X-Y co-ordinates easily...
I regard the DRO on my mill as indispensable. It doesn't enable the mill to do anything it couldn't do without it, but it does make it much quicker and easier for me to get things right the first time.
I'm just an amateur HSM crank-turner so production and efficiency are absolutely not issues, but I sure like having the machine cut where I think it's cutting.
For hole patterns, I never do a layout even in sheetmetal. I just make a CAD drawing with ordinate dimensions, then go dial in the numbers and pull the quill -- digital drillpress.
Trust me, it's worth it. Without one, particularly on a really old or poorly maintained machine, it's a lot harder to make accurate parts. Plus, there are other factors other than backlash that can ruin measurements off the dials. I have a 3-axis (knee) Newall on my machine, and after it was installed, I realized that tightening the knee lock often moved the measurement 50 thou or more. Now I can get really accurate measurements in all sorts of setups. In terms of specific features, pay a few extra bucks for a good one with bolt hole circles, datums, and other features. It'll save hours in messing around with the machinists handbook, trying to figure out the x-y coordinates for some weird pattern. My DRO also has a line feature, which is like a bolt circle except it is a number of evenly spaced holes on a line, and you can set the line at an angle to the travel. It also has a arc interpolation, which allows you to rough out an arc to 5 thou or so. Not CNC, but if you need to have an arc on the corner of a part to clear another moving part (a situation I've run into several times), it's pretty useful. On two versus three axis, buy a 3 axis knee model. That will probably be the most useful setup for 99% of the work the average user does. As far as models go, I really like the Newall because of its useful, intuitive interface and non-contact scales. Unlike the other models, the Newall uses induction to measure against a stainless steel tube filled with ball bearings. That means that the read head (the sensor part) is completely sealed and doesn't need to mechanically contact the fixed scale. It slides around the outside of the tube like a linear bearing, but there is not sensor that physically contacts the scale, which drastically improves reliability. Hope this information is useful, ww88
Your mind and fundamental skill level will improve without one. I had to do several hundred hours of manual milling without one, and I'm better for it.
However, if you just want to make parts and you're not trying to make a living as a machinist, then get a DRO with your machine. They're light-years behind having a CNC machine, but light-years beyond a manual machine without (in terms of speed, not really accuracy).
I've used a number of Heidenhain units on mills, lathes, and grinders. There's a bit of a learning curve if you want to use the fancy features, but otherwise they're fairly straight forward, and seem to be quite reliable (and accurate).
Most DRO's are non-contact, using optical scales with intrinsic resolution of typically 50 microinches though the DRO may only resolve to half a thou.
I find 2-axis quite sufficient, don't lust for a Z axis. Z excursions are typically rather small compared to X and Y, so a DI works just fine and I rather prefer it for some reason. YMMV.
That is BNC. Biological Numeric Controlled. Not that much CNC.
If your pride allows it, buy a DRO. It will save you time (often enough a lot). You'll have more accuracy (backlash with worn leadscrews) Reduce errors (lost track of counting revs, complex patterns)
I think this is what my older brother, who is a pro, would say. Or more likely something like they you don't tell you everything. Since I'm a HSM, I'd rather do what is easier.
I've done it too but I also layed out intersections and edges using bluing and a height gage just to keep me from losing position by losing count of turns and such. I really don't ever want to do that again if I can avoid it.
I have to weigh in on the "maybe not" side. I 'borrow' one of two Bridgeports in the lab at school, both have 2 axis DRO's plus the add on spindle readout. Marvelous to use, so much easier to do all the common things like spaced holes and accurate slot widths.
But if I get a mill for my home sh> I believe I am ready to take the plunge and replace
Money well spent. If you have a CAD program, you can calulate bolt circles, etc. into x-y cordinates that you can easily crank in. Also, when you have to do several operations on a series of holes, you can go from hole to hole with each tool, then change tools, etc., because it's so easy to relocate. With older eyes, it's a lot easier to see the readout than to read the dials.
I have to relate a conversation I had with a friend, a master machinist who owns an EDM shop and has a couple Bridgeports he uses for making fixturing. I mentioned to him another buddy of mine who has a CNC shop and a couple old Bridgeports that have dial indicators on them unstead of DROs. He commented, "Well, I hope he has snow white hair, because if he's any younger than that, he doesn't know how to use them." Interestingly, the guy with the CNC shop rarely used his manual mills, doing everything on one of the CNC Workcenters, even the "one ofs" that would be much easier on a manual mill.
If you absolutely HATE computers, and will absolutely NEVER want CNC, then a DRO is a great thing to have, as the leadscrews start out with backlash, and later develop non-uniform wear, so even when you stay on the same side of the backlash, nothing will be accurate.
But, since you are on this newsgroup, you probably appreciate what computers can do for you. A commercial 3-axis DRO will cost $1500 even at a good discount. If you are going to pay that much to get the limited functions of a DRO, why not spend just a little more, (and I do mean little) to get full CNC? Will you be buying a decent rotary table for the mill at some time? With CNC you will have no need of a rotary table. The cost of the rotary plus DRO will buy you the parts to go CNC!
You can then design stuff with curves and straight lines not parallel to the machine's axes, and cut them as easily as a straight line that IS parallel to the axis. It probably is hard to visualize this until you have done it and seen how simple it is, but it is like having blinders taken off when you can do something simply that was a royal pain before.
If you have a decent "junkbox" with some larger, old stepper motors (or even servo motors) then the CNC conversion can be even cheaper. You can also buy machines with ballscrews on them from the factory. Or, pick up a dead Bridgeport BOSS machine and put a PC on it to make it run again.
I have a well-worn Bridgeport, circa 1938 (originally with M head, round ram and 9" Y travel.) When it still had the original Acme screws, I had all sorts of trouble with it. I found an ancient Bridgeport optical readout unit ( etched, mirrored glass scales and magnifying projector boxes with vernier) and got that installed and working. I then found out how badly the screws were worn. I had .030" slop in the middle of the X, and .050+ in the Y. But, about half that wear was in the nut, the other half was in the MIDDLE of the screws! So, if you moved from one end of the X to the middle of the travel, it would actually be about .015" short, even if you took care to approach both readings from the same direction. Of course, once I put the optical unit on, those errors could be eliminated. Suddenly, if I made a box and a cover, the holes would line up without filing the holes egg-shaped! Wow, amazing!
Unless Harold has a Morse Jig Bore, or something else with excellent and wear-proof screws (or ballscrews) on his machine, there is no way to do accurate work using Acme leadscrews and the dials.
Well, a few years later, I upgraded from the 1960 technology of the Bridgeport optcal readout to CNC. I still make mistakes every once in a while, but I get what I want much more often the first time with the CNC than I used to do with manual machining, DRO or not. I do a lot of control panels with odd-size slots and cutouts, and it is really aggravating to spend several hours making a panel, and then go past the mark (or coordinate) on the last few cuts and ruin the thing. That rarely happens with CNC, and if it does, you fix the wrong number and run it again, and the good part is done in
15 minutes, even when you have to make the 2nd piece to get it right! (If I take the time to double check all my coordinates, then there's no need for a do-over.)
I'd NEVER. EVER, go back to manual for most of the stuff I do. The CNC is so much better in every way. On the other hand, I did learn a lot about the "feel" of metalwork on manual machines, and still use that when CNC'ing. That's something you can miss if you go straight to CNC.
If I just need to drill a hole "about there", then CNC and DROs are not relevant, and the manual quill handle is a lot faster. But, for one-off carving out a pocket or all sorts of other things that require a number of linear passes, the CNC can still be a lot faster, if you have a good system for entering the motions needed. Making a full CAD drawing can slow you down, but in most cases that is NOT needed to get the G-code.
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