Help building drilling jig / fixture

monkey123 · Oct 22, 2012

Hi there!

I am looking to build some production jigs/fixtures for drilling die-cast aluminum enclosures on four or five faces. I've done quite a bit of research and planning and have finally found what I believe to be the best option for me. What I need help with is tips for assembling these fixtures, as I am very new to metal working with a limited tool set. However, I can purchase new equipment (within reason) and have a steady hand with great attention to detail. The reason I'm not simply having a metal shop do this work is that the ones in our area have been very flaky and we can't seem to get them to actually do the work for us...

The fixtures will be made of 1/2" thick 6061 Aluminum. There will be a top face with about 3 sides. The enclosures will drop in the back side and be held in place by alloy dowel pins, and lock into place with a bit of an aluminum lock that slides into place. The dowel pins must be super accurate to get a snug hold. The 3 sections of aluminum will have holes drilled in them with press-fit bushings to be used as drill guides. Drilling will be done with your average drill press for production, and there will be a gap between the fixture and enclosure to let chips escape.

My questions:

I have a standard drill press, bits, cross-slide vise, digital calipers, center punches, etc. I will print out a template for the holes on the jig and tape it to the aluminum before making center punch marks. What is the best way to achieve the most accurate hole positions? I need accuracy to about 1/2mm.
For a bushing that has a listed outer diameter of 3/4", how should I drill that hole? I've read many differing opinions. Best I can tell is to drill it to size and use a C-clamp to press the bushings in?

Any other tips for this are greatly appreciated and I'm sure I'll have some more questions as I think some more. Thanks so much!

monkey123 · Oct 22, 2012

thermite said:
WHICH bushing (system) or type do you plan to utilize? Have you chosen a drill? And do you plan the use of any drill lubricant or coolant? Do you have shop air at the machine? Regardless - a 'C'-clamp has no place in the equation. They ALWAYS pull to one side or the other.

Bill

I'm going to use a mixture of McMaster Press Fit and Press Fit with head bushings. What do you mean about the drill (sorry - new to this)? Are you referring to how I'm drilling the jig hole? I was going to use my regular drill press, probably titanium coated Dewalt bits. Didn't have a plan for lubricant as I've never needed it before while drilling metals (gasp), but the plan was to drill slower. I do not have air available.

monkey123 · Oct 22, 2012

Thanks for the tips. Any advice on the drilling for the actual making of the fixture?

Also, I'm open to other metals for the fixture frame if there are better options. I was going with the 6061 aluminum due to 1) cost 2) easy machining 3) have had previous experience with it.

hickstick_10 · Oct 22, 2012

Why are you making it out of aluminum? Schools have students make their drilling jigs out of aluminum for projects....................................................................

But its not the greatest thing to have if you want a good wear resistant jig.

wr4t · Oct 22, 2012

If you want tips on how to layout accurate holes with manual methods I recommend this book (free ebook), I know it is old, but it does cover precision layout, drilling and boring.

Accurate tool work - Clarence Leon Goodrich, Frank Arthur Stanley - Google Books

It covers the techniques necessary to layout holes to .0002". A surface plate, and height gage would be strongly recommended. If your holes only need to be located to 1/2 mm or .020" (hard to beleive you have this much allowance if you are using dowel pins for locating). You should be able to get by with a combination square and scribe, with practice 1/64" (0.16) is easily attainable. However I still recommend a surface plate and height gage.

Good Luck

WizardOfBoz · Oct 22, 2012

monkey,

Your post and question were quite clear. Thermite's response compresses a lot of experience into a concise, information-packed posting. Read it and heed it.

There's a couple of questions. The accuracy question is touched upon, above. The other question is: how many pieces do you anticipate making? Is this a hobby deal where you will make 50 parts, or a commercial idea where you will make 500, or an ongoing 5000 part/year operation?

If you do use thermite's clever "no bushing" idea one possible suggestion is to chamfer the entrance hole slightly, and smooth and polish it with some emery paper prior to hardening. If you look at a drill bushing, they're rounded and very smooth - facilitates the drill entry and avoids the drill hitting a rough, sharp edge of hardened A2.

monkey123 · Oct 22, 2012

bosleyjr said:
monkey,

Your post and question were quite clear. Thermite's response compresses a lot of experience into a concise, information-packed posting. Read it and heed it.

There's a couple of questions. The accuracy question is touched upon, above. The other question is: how many pieces do you anticipate making? Is this a hobby deal where you will make 50 parts, or a commercial idea where you will make 500, or an ongoing 5000 part/year operation?

If you do use thermite's clever "no bushing" idea one possible suggestion is to chamfer the entrance hole slightly, and smooth and polish it with some emery paper prior to hardening. If you look at a drill bushing, they're rounded and very smooth - facilitates the drill entry and avoids the drill hitting a rough, sharp edge of hardened A2.

This is an ongoing commercial application. I'd expect the fixtures to be good for 1000+ parts.

I'm not sure if the dowel pins need to be tapered, as the enclosures are tapered slightly and should get a snug fit that way?

I've mentioned before that there will be plenty of space for chips to escape in the fixture. The aluminum enclosures I'm drilling in the end are only 1/16" thick so there won't be that much metal flying. I'm also not concerned about scratching parts as they will be painted after drilling.

RJT · Oct 22, 2012

If you have no experience in drilling , boring, reaming, for press fits of dowels and bushings, you should not be attempting this. A good precision drill jig for thousands of parts is well worth the money to get it made correctly. Find a better shop, you will be way ahead in the long run.

Robert Campbell Jr. · Oct 22, 2012

Unless my lack of specific knowledge of the part is leading me astray.....

Most drill bushing fixtures have no provision for internal support of hollow work pieces. Your enclosure-type of work piece made of 0.0625" wall material will distort under the drilling pressure without internal backup. It is likely that some provision must be made to counter that, unless some distortion is acceptable.

Under the right, (wrong) conditions, the distortion could be wide spread, IE: the famous grab-and-twist move well known to dancers.....

From your above description of performing work on 5 sides in one set-up, internal part support sounds like a real challenge. A drawing or rough approximation of the part should get you some good suggestions to alleviate that potential condition. Could be as simple as a loose "cube" with drill clearance in the appropriate places, accurately located/immobilized by some feature of the fixture.

Bob

monkey123 · Oct 22, 2012

The enclosures are powder coated and defects on the aluminum have never been a problem previously. The paint will never peel or chip if coated properly and it does not reveal defects in the part. Given what we are going for, drilling is the most realistic option for us instead of punching. Once these fixtures are setup they will be very quick to drill. Attached is a picture of basically what I'm designing - I came across this on another site and the enclosures look to be very similar. Hopefully this is very helpful and clears up any confusion.

Robert Campbell Jr. · Oct 22, 2012

monkey123 said:
The enclosures are powder coated and defects on the aluminum have never been a problem previously. The paint will never peel or chip if coated properly and it does not reveal defects in the part. Given what we are going for, drilling is the most realistic option for us instead of punching. Once these fixtures are setup they will be very quick to drill. Attached is a picture of basically what I'm designing - I came across this on another site and the enclosures look to be very similar. Hopefully this is very helpful and clears up any confusion.

View attachment 61469 View attachment 61470

That should help a lot, even providing information with which to provide drill bushings for five sides, as opposed to the three in the pics. Also, clearly a die-cast part, which might well be stiff enough to resist distortion without internal back-up, though that could be provided for in the illustrated pic's too.

Bob
Edit: and there it is, right at the top of your first post, "die-cast aluminum"

monkey123 · Oct 22, 2012

Yep, die-cast. They are very sturdy boxes and would take a lot to distort them. I can't imagine the drill pressure I'd be applying could do that easily.

I want the fixtures to be good for 1000+, but each individual run may be 25-100 at a time. We're going more for a pull system where parts are drilled as they are ordered, more or less.

Bikerat · Oct 22, 2012

I'm a red neck that sound's too complicated to me. I'd just make a jig to use a spring center punch to mark hole area and drill with a cordless.I like tenth's.

monkey123 · Oct 22, 2012

Bushings will be color coded. Everything involving tooling in the shop is, so it's easy to spot which drill bit or socket goes on what.

Sea Farmer · Oct 22, 2012

I have found this book to be an excellent guide: "Jig and Fixture Design Manual" by Erik Henriksen, Industrial Press, Inc., 1973. ISBN 0-8311--1098-8.

monkey123 · Oct 24, 2012

Does anyone have recommended speeds for drilling aluminum with a drill press? What speed for 1/2" 6061 aluminum? What speed for 1/16" die-cast aluminum? I'm using average wood/metal drill bits. I don't mind going slower if necessary and the bits stay a bit cooler...

72bwhite · Oct 24, 2012

Drill speed is dependent on bit size, bigger bit slower speed.
Don't have a drill press so I just use the mill and being lazy usually just shift to low range, so either 240 or 150 rpm more or less, for the larger holes you would do better drilling a pilot hole.
Maybe even going in 2 or 3 stages, thin like that twist drill love to grab and try to lift the work piece.

monkey123 · Oct 24, 2012

Yes, I will drill pilot holes and larger holes in stages. Parts will be clamped in a vise. I found a chart on fnal.gov that recommended 1,000-3,000 rpms depending on bit size. http://www.fnal.gov/pub/takefive/pdfs/Drill_Press_Speed_Chart.pdf

monkey123 · Oct 24, 2012

My plan is to print out a template with hole markings, tape to the aluminum plate, mark hole centers with a carbide scribe, then mark the scribed marks with an automatic center punch, then drill small pilot holes and then work my way up to the correct hole size. Do you think this will get me the most accurate hole centers with just a drill press and cross-slide vise?

72bwhite · Oct 24, 2012

yes that would be about the same way would do on a mill, mark it clamp it in the vise then line it up with feeds.
A center finder will get you better then eyeballing it they are cheap 5 or 6 bucks maybe but for your purposes eyeballing it would probably be ok.
Aluminum gets sticky when it heats up while you drill so some oil is helpful I was doing holes in a plate about like you are drill just a couple days ago 1/2 in. was my pilot hole sharp bit 150 rpm light pressure swarth came out as a nice spiral.
If the bit chatters you are spinning it to fast.

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