Finally I need to make something to good precision, which is to make a mounting plate for a US Digital encoder. The spec says shaft misalignment should be under 0.01", which means that the individual mounting holes need to be even more precisely placed, so as the cumulative error will stay within spec.
Anyway, step number 1 is to cut a 4x1/4"x12" aluminum flat into three pieces. I would like to do this on a Bridgeport and to use a thin endmill, so as to keep as much material as possible. Should I use carbide or HSS and what speed would you recommend for, say, a 1/8" endmill?
Second question, I will need to tap #4-40 holes in same aluminum. How risky is this as far as tap is concerned and should I use lubrication?
Ignoramus13320 fired this volley in news:7oednW7KGcIsVobRnZ2dnUVZ snipped-for-privacy@giganews.com:
In revers order, Iggy: Yes, you should lubricate the tap, and in a hole that deep (which is deep for 4-40) you should not try to power through in one pass, but back it out and clear chips several times.
On the first part: it's no risk whatsoever to the tap, so long as you don't torque it to the breaking point .
Whatever you do, don't try to freehand tap those. Even if you don't use power, use the mill with a center chucked in it to keep that tap straight over the hole the entire time (if you're using a tap wrench), or just chuck up the tap and use your hand to turn the spindle. Off-line tapping breaks more taps than the character of the metal being tapped.
Slicing up plate with a small endmill is a lousy way to go. Better to cut with a bandsaw or even hacksaw and then finish mill the edge with a decent sized end mill (.5"+).
Tapping small holes is very risky. Do the complete process for each hole without moving the mill X/Y. Load up your chuck in the spindle, put a small center drill in the chuck, lock the X and Y and spot the hole. Change the center drill out for the appropriate tap drill and drill the hole, using a squirt or two of Kroil (or other suitable lube) as you peck drill. Change out the drill bit for a spring loaded tap center (ENCO, MSC, etc.) with a point that will rest in the center hole at the back of your tap handle. Load the tap in the tap handle, rest the tip of the tap in the hole and bring the spindle with the spring center down to rest in the back of the tap handle, compressing through most of the spring travel. Apply a few more squirts if Kroil and begin tapping, 1/2 turn in, 1/4 turn back, gradually progressing. If the hole is deep, periodically back the tap most of the way out and blast if clean with air, relube with Kroil and continue. Doing all of this in one sequence with the X and Y locked ensures you remain on center and avoid side strain that would break the tap. When one hole is complete, unlock the X and Y, locate the next hole position and start the process over.
Not certain which US Digital encoders you are using but here are some being installed directly to tiny motors (no plate). One way to achieve accuracy with this encoder type is to use the centering tool with double sided tape on the plastic plate then use the plate as a drill template.
Hand tapping machine (Enco) and Tap Ease "crayon" was used for tapping. Also, flat instead of pan head screws were used only for neatness. The supplied pan heads work just fine. Pictures here;
OK, the task is to cut a 12 inch long chunk of aluminum into three pieces that need to be square and as large as possible. (not quite what you said but this is what I think you mean.
The problem with using an end mill to make a really thin cut is that the smaller the end mill the easier it is to overload the cutter and have it flex.
What I would do is to use a skill saw or a band saw or a jig saw to make the cuts and then square them up with the mill. If the saw kerf of the skill saw is 1/8 you will loose 1/4 to 3/8 over all. that means you end up with square plates 3 7/8 finished size. If that is not good enough then go buy some more aluminum.
The skill saw technique will be to attach the plate to a chunk of wood that has a stop affixed to it. Now to this you clamp a saw guide that you can hold the guide of the skill saw against and keep everything as square as you can. make one cut from each side after marking lines to delineate the outer limits of what you are willing to go.
Now once you have the three blanks you can then square them up and size them on the mill.
If you don't have a skill saw (or a table saw) the band saw or the jig saw can be used if you mark the lines with a caliper and then carefully cut between them.
The 4-40 tap will work fine just drill carefully (center drill, then tap drill) and then use aluma-tap and go easy.
When you size and square the plates, be sure to tram the head of the mill and then indicate the vise. Doing that will get you as close to dead nuts as you are going to get.
Sounds like you don't have a bandsaw. A tablesaw or chop saw (depending on cut direction) is perfectly capable of cutting aluminum. Hack saws work too, this is aluminum.
The other day my uncle called me to tell me he stopped over and borrowed my chop saw to put up some crow molding. I asked him how it cut, he indicated it cut fine, that is when I told him I've been using the blade on it to cut 80/20 and other aluminum extrusions for years. Wear ear and eye protection.
Is it possible to mount it in such a way that you can adjust the location? 0.010" is not that tight a spec anyway. If it were 0.001" that would be a bit more trouble.
Don't you have a bandsaw? You could use a bandsaw to make it just a little oversized, and then the mill to clean up the finish on the edges.
No need for carbide, and it is a lot more brittle.
You probably want to add only a 1/16" depth of cut for each pass (half the diameter of the end mill). It should be a two-flute one so it is center cutting, and so cutting forces are less likely to deflect the sides of the mill into the sides of the cut. (The greatest deflection force on a 2-flute end mill is when a flute is passing across the direction of travel -- and with a two-flute, the other will be behind the mill where the already cut space is.) If you get deep enough, you will have part of the flute twist around to the sides.
The Brits call a two-flute center cutting end mill a "slot drill" because it is so good for this task.
You'll want to have compressed air blowing chips away from the groove so they don't keep getting re-cut. (Or a shop vac nozzle right beside the cutting location.)
Perhaps use something like WD-40 as a cutting lube if you can't clear the chips as you go.
Depends on the tap -- and the grade of the aluminum. If it is something like 6061-T6 it should tap and mill nicely. If it is a plain mild aluminum it will gum up both the end mill and the tap with likely disaster to both.
For mild aluminum, you probably want a thread forming tap (displaces metal instead of cutting it out) and a different size tap hole than with a cutting tap. (_Machinery's Handbook_ has a table which gives the right size for that.)
For the 6061-T6, use WD-40 as a threading lubricant or the TapMatic marked explicitly for Aluminum (absolutely *not* the original formula -- if you can find it -- which attacks the aluminum).
And Ideally, you want to use a "gun" tap (spiral point tap) in a tapping head in the drill press or the mill for tapping through holes. That is designed to chase the chips ahead of the tap, so you don't have to keep backing up the tap to break the chips. Regular (plug) taps are more of a problem -- especially in soft aluminum. If you don't have the tapping head, a hand wrench and a guide to keep the tap perpendicular to the surface of the workpiece.
tap guide, 325-5179. The pin is spring-loaded and reversable, the other end is pointed. It says for #10 thru 1" taps but I've used mine with taps down to 00-80. I use it both at the mill and at the lathe. I about never tap a hole without it.
I've got one -- and was just using it downstairs in the shop within about the past hour. It was on the lathe with the bed turret in place, so I swapped it into the drill chuck on one station which had just drilled the hole to be tapped.
It is very nice as long as you have not shifted the workpiece with respect to the spindle since drilling the tap hole.
But for multiple threaded holes on the drill press I am more likely to use a TapMatic tapping head with gun taps. It (the larger of my two) was a lifesaver when I had to drill and tap 24 holes for 1/4-20 in 1/4" thick steel plate. I also had to be creative in supporting the fairly long (24") workpiece when drilling and tapping the holes near the ends.
We're amateurs, John. I occasionally machine-tap in my BP or lathe, but usually hand-tap using the tap guide. I can feel the torque, know if/when a tap is in trouble. Production isn't an issue in an amateur's shop. The quality of the job has nothing to do with whether the motive power for the tap came from a machine or the machinist.
OK, but where does one purchase a small quantity of this stuff? Goo-Gone is as readily available as WD-40.
I never do it in a drillpress, always in the BP. The DRO makes it easy to return to a hole for tapping if it isn't tapped immediately after drilling. If the holes are close together it's quicker to drill them all, then go back and tap them all. If they're further apart it's quicker to change from drill to tap at each location.
I once watched a machinist tapping hundreds of holes in what I think was a prototype Mark 46 torpedo. He did it with a pneumatic hand drill. Zoop zoop, slick as snot. I suspected that he'd done this before.
A pneumatic drill isn't nearly as likely to snap a tap as an electric drill. If the tap gets in trouble the pneumatic drill will stall, saving both the tap and the job. It still takes a steady hand, though. I've done it with #10 and 1/4" but I wouldn't try it with 6-32 or smaller.
An ordinary battery operated drill works fine in most cases, especially ones with a clutch.
The 6-32 tap tends to break just looking at the thing, but that is not due to it being a #6 screw, it is due to the ultra-course pitch. 6-40 works much better.
I've got an American made unit that I picked up from a local tool supply house for $20.00. It only had the base and arm. The shaft was missing so I made one. The unit would be a good project for a HSMer and they are very sensitive all the while holding the tap properly. In a pinch you can even drill with one of these. Amature or not, Iggy is going to live with this job for a long time. I'd look at the job from that perspective when planning it.
New, they are a couple hundred bucks or more but I used to see them in a lot of places that had manual machines and did a lot of small production holes. I believe they were even called "Sensitive Tapping Machines".
I get eight ounce containers/bottles from Northern Tool's online store. Not cheap but it lasts a long time. I've got two bottles that I purchased to tap 4-40's in A267.
IMHO WD-40 is just awful. I won't use the stuff for anything. Well, it can be used as a local anisthetic but I wouldn't recomend using it for this purpose very often. Any time you want to rust the mating surface between a milling vice ( or anything else ) and a machine table spray some WD around first.
It's good for spraying under your lawn mower to reduce the stickiness of the grass that most of us are too lazy to clean out. That, and cleaning wrenches and some other hand tools, are all I'll use it for.
Oh, in a pinch it makes a half-decent starter fluid for balky weed-whackers.
A speed wrench makes a GREAT quick tapping tool. I pressed a tap holder with the handle removed into a 3/8 drive socket, 12mm IIRC. Put this on the speed wench with your tap installed and go to town!
If I'm drilling on the manual mill, I use the same tool you suggested. Course, i prefer the cnc mill. Iggy's job would only take a couple minutes if he had his CNC mill running.
He needs to purchase a centering tool (CT) or make one. IIRC, they do not come with the units. It's just a tapered bushing matching shaft size (internal diameter) and encoder mounting plate opening (tapered external diameter) that centers the device around the shaft so you can drill the holes within reason.
Hole locations do not have to be as precise as the OP is implying. You use the CT again to center the encoder ***precisely*** while tightening the screws. Installing a US Digital encoder accurately is really a piece of cake. In fact, dual shaft PM motors from CNC suppliers these days typically come with holes either drilled directly in the motor or on a plate attached to the motor, meeting Agilent/USD mounting specs.
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