Reaming aluminum

[ChrisAttebery]

Hi guys,

I'm going to try reaming some 11/32" x 2" deep holes in aluminum for needle bearings.

I've never used a reamer before. I know that you should drill to 1/64" smaller than the reamer, but what speed should I use? Should I ream them by hand? I'm assuming WD40 or aluminum tapping fluid should be used.

Any input would be appreciated!



Chris

[Victor_R]

Chris,

You've not given much information as to size of work piece, type of aluminum or whether it's a through hole or blind. So this makes the answer longer.

If at all possible, boring is the best way depending on the size of the work and machines available. So I'll assume that you can't bore. (Yes I know 11/32 is small, but there are ways.) Boring gives the best finish and size control.

If you must ream, do it in a machine. Lathe or mill is first choice. Drill press if those aren't available. Hand reaming is not the first choice because you don't have good control.

Hopefull you have a nice tempered aluminum. If I had to ream this hole I'd use a nice sharp ream that was evenly ground. (As in new) I'd make it as ridged as possible by cutting the shank if necessary. And I would take off less than 15 thousands as a final pass. Since it's a small hole I'd use a fast speed and a slow feed by hand. And yes a cutting fluid would help. Not for cooling but for surface finish.

If you're working in a blind hole, chip build-up will be a problem. You'll have to remove the ream several times to get the swarf out. That's why I would want a very light cut as a final one to help with the surface finish.

If the needle bearings are going to be in contact with the finished hole, I might consider some way of honing to the finished size.

Victor

[J_Tiers]

I assume the bearings will have a liner to run on?

I don't think needles running on aluminum, and reamed slightly chattery aluminum at that, will work very well.

[ChrisAttebery]

Victor,

You're right I should have given more info, but your answer covered my questions.

The hole was in 6061 -T651 and it was all the way through. I used a 21/64 drill for the first pass
and then used the reamer with the spindle speed at 2500 rpm. It chattered just a bit when I entered
the hole, but it came out very clean. I flooded the hole with WD40 through the whole process.

The bearings are in a shell .343" diameter by .375" long. They will be pressed into the housing.

Thanks for your help,


Chris

[doug925]

Hi Chris. I am glad to hear that you had no porblems reaming the bearing holes.
When i ream Aluminum, I use a 90 sfm, and .006 feed per rev.
example rpm=3.82x sfm(90) / dia. (.500), or 3.83x90/.500 = 687 rpm x .006 ipr(inches per rev.)=4.125 inches per minute.
I drill 1/64 underneath the ream hole size (just as you did). when reaming that deep you need to "peck" the hole. Which means pull the reamer out , and get rid of the chips a few times during the length of cut. Do this with power off!! If you back out a spinning reamer, it will cut coming back out of the hole...You will get an oversized hole that way. Best of luck.
Doug.

[MikeG]

Hi Chris
As a rule of thumb, the ream speed is usually 1/2 to 2/3 the speed used when drilling the hole

MikeG.

[ChrisAttebery]

Mike,

Thanks, I'll keep that in mind for my next project.



Chris