Step by Step Hole Reaming Instructions

[David Doerr]

I've encountered the same problem with our team. We're working in my basement where we have a 1940's Boice-Crane drill press and several other machines handed down to me from my grandfather. It has a 1/2" chuck and the speed can be varied over a wide range.

Here's what's worked for me...

We have two adjustable reamers -- size "G" for the .875" holes, and size "I" for the 1.125"s. Along with those we have two reduced-shank drill bits - 55/64" and 1 7/16". You can pay $$$ and get these at someplace like McMasters or you can do what I did and pay a lot less on ebay or grizzly.com. So far the imported tools are working out OK.

Clamp the workpiece very securely and - as was recommended above - drill a 1/64 undersize hole. You'll need to set your drill press to turn at two or three hundred RPM and you may want to start with a pilot hole. Go slowly when drilling the hole.

The reamer will be too big to chuck in the drill press, but you don't want to do that anyway. Manual reaming is the way to go here. Normally you'd use a large - and expensive - tap wrench to turn the reamer after inserting it in the drilled hole. But, you've already got a handle in the form of the rail you're working on, so why not use that?

Clamp the square end of the reamer in a vise so the reamer points up. Now you can easily adjust the reamer so the cutting diameter is a few thousands less than the bearing diameter - use a micrometer or caliper to check the adjustment. Then with the reamer still clamped in the vise lower the rail onto the reamer turning the rail in the cutting direction only. This will only work, of course if you're making two holes all the way through both sides of the rail. The advantage is that the two holes will help you keep the rail perpendicular to the reamer. Unclamp the reamer from the vise to remove the rail from the bottom when you're done reaming.

I found that one reamer pass with the 1/64 undersized hole seemed to work well.

It's a trial and error process to get the best reamer adjustment. Test by installing the bearing, then tweak the reamer adjustment and start over with a newly-drilled hole until you've got it right. If you go to a different material - polycarbonate, for example - you'll need to re-adjust the reamer for that material.

Note that I'm a novice machinist and I'm no mechanical engineer, so take my advice with a grain of salt.

Another option I like that I haven't seen mentioned is a Greenlee chassis punch. They cost $$$, though. Also, like the hole cutters already mentioned, you end up with a loose bearing fit. If you want an interference fit you need a reamer (or one of the other options that require more sophisticated machinery).

[Tom Line]

Originally Posted by Cory

In a production environment I'm guessing you would have some kind of offline fixture that would allow you to adjust the boring head to the right dimension with no trial and error.

We don't bore a ton of holes in production, but we set up all our tools offline with four of these:

http://www.zoller.info/usa/products/...es/»venturion«

Accurate to micron levels.

[craigboez]

Originally Posted by sanddrag

Lowes sells Ideal brand hole cutters in 7/8 and 1 1/8 sizes. We have the 7/8 one we use on occasion for prototypes. It works well. I don't recall the exact hole size it comes out with, but in a drill press I recall it being .005 bigger or less. It would be better in a mill. It makes a nice clean round hole that works fine with flanged bearings.

Found this:
http://www.hougen.com/tech_tips/cutt...hole_size.html

According to Hougen, if you have a rigid setup there is a high probability that your hole will end up somewhere between +0.0005 and +0.0035 from the nominal drill diameter. Sounds pretty good for a flanged bearing looking for a slip fit.

[Spirator]

We've been doing exactly this. We use a 20mm chassis punch and then ream the hole to 22mm and deburr until we get to the proper press fit tolerance. It works very well and the bearings haven't come out yet. It takes around 10-15 mins per press fit.

No machinery required.