[peter.blais]

Hi guys.

I've got some parts which are made of 1/4" 6061, and machined down to like .2" .

Anyways, the stock is wide enough that if you hold it between vise jaws, it vibrates like hell.

To combat this, I made a 24" long plate out of 1" thick 6061, 8" wide. I machined the center out and have a slot full of pitbull clamps holding down two 3" wide strips of stock.

Anyways, I really thought this would give me a nice finish, like when I machine nice thick stock. The stock doesn't have much evidence of chatter- and there's no sound, but the face mill marks up and down the plate are inconsistant.

Anybody have any insight about this? I'm thinking perhaps I got a little carried away with the pitbull clamps, and I'm bowing the plate up slightly- but I played around with the torque on the clamps a bit and it doesn't seem to make any difference.

I'm afraid of having the stock come out and wrecking my favorite face mill lol.

I'll post a picture of the setup tomorrow at the shop and the results.

[Matt@RFR]

What style inserts are you using in your facemill? What DOC, speed and feed are you using? In my experience, the absolute worst thing you can do in your situation is feed a facemill too slow.

There is a lot of talk lately of very poor aluminum being sold. Could this be part of your problem? Do you have any other 1/4" thick material that you've had good results with, that you could cut down to your current size?

Also, you might post a picture of the finish you are getting.

[austin.mn]

I do a lot of thin stock machining. You need to tape it down with carpet tape, then clamp it. It should make a big different on your finish.

When I first started engraving thin aluminum, I would break tiny bits on the finish pass. For some reason no matter how light I program the cut it was always way to deep. I found that when you relieve the stress on one side of the material it will tend to bow upward. If you stick the part down with a little double sided carpet tape it will keep the material from bowing and keep it from vibrating.

[dougtyler]

Google the name "mitee grip"

Its a waxy type material that you can use to bond your part to a sub plate.

This stuff works awesome. just heat up your subplate and part to 200 degrees. (I use an electric grilled). Then place the part on the subplate, apply weight to keep it held down while the assymbley cools off, and your good to go.

This stuff has a holding strength of 40 psi.

When your done machining just heat it back up to 200 degrees and the part will fall right off.

[hitachibos]

i have done alot of this type of work and i agree with Austin.mn use TAPE. but there is a secret to what else he is saying. "I found that when you relieve the stress on one side of the material it will tend to bow upward."

what you need to do is find the natural bow in your material put 2 strips of 2" tape on a subplate that is flat and clean (use alcohol to clean the plat and stock)

lightly place your part on the tape so the edges bow upwards. (like a bowl)

The middle will stick to the tape. Now in the corners at least, place shim stock under to take up the air gap. (you can do the edges too)

Cut the surface but only clean up the top to about 75% clean <- i mean most of the surface will be cut and some will still be raw material. THIS is the key IF you cut the whole surface now it WILL BOW

Spray alcohol around and under the part to loosen the tape.

now put tape on your part first where it took a chip and cleaned up.
place your taped part down on the subplate and cut this side complete until you clean the whole surface.

unstick it and flip it one last time use tape again and bring you part to thickness. cleaning up the origonal side you started with.

if all goes well you will have an extreemly flat piece when done with NO bow.


Good luck.

[hitachibos]

remember 3 flips for flat

[peter.blais]

Here goes:

The face mill is a mitsu. ASX400 with their HTi10 aluminum inserts in it. It's a 4 insert 2.5" cutter and feeding 80ipm @ 3500 rpm for finishing. This has given excellent finish on thicker material. I tried faster / slower on the feed and rpm, nothing seems to improve it much.

I don't think the material is an issue. It's from a local extrusion house about an hour down the highway- we've machined a lot of it in thicker form and not had any issues. I did make some parts a long time ago using some thin alcoa, and it was fine. I held them differently though.

I'm a little leery of tapes / adhesives because I was sort of figuring this out for an upcoming run of 1000pc of something else... I don't really want to be heating / cooling that many pieces or "trays". I suppose if I made a sub plate / dowel pins setup, I could be heating / cooling while the machine runs.

To the gentleman who suggested carpet tape- what is your procedure between batches?

In the past, I drilled extra holes in the stock, in areas which would be machined through later- and then used flat head allens just below the surface, and this gave excellent surface finish. It's also a pain in the ass as those bolts need to be removed and the parts secured down through the permenant holes for machining the profiles etc.


I attached the pictures of what I'm getting. The actual finish isn't bad, but I can tell the part is deflecting because the tool lines move around on it. I haven't spent a lot of time with a mic on the finished part but i can only assume the finished part also includes high / low spots to some degree. I did check quickly and the parts produced would be acceptable, I'm just not happy with it.

I did try a few different torque settings so to speak on the clamps. I'm afraid of loosening it up any more and having it pull out & wreck my inserts / face mill. I've never used the pitbull clamps before so not much experience here on how tight they need to be.

[peter.blais]

PS: The piece of stock shown is from before the fixture had those extra drill holes and circles machined into it. I'm facing one side, then flipping it over and facing / drilling / pocketing.

[BobWarfield]

You can also use superglue. Heat will make it release, but use good ventilation, because the vapors are toxic. It's very fast to lay down superglue.

A vacuum fixture might also work for your application, but it would be more trouble to make one. Still, for 1000 pieces, it might be worth it.

Cheers,

BW

[osphoto]

Thank you for the suggestion of mitee grip!

[fuzzyracing1967]

Something else you may want to try, since you mention 1000 other parts, would be to make vice jaws that are the length of your part. In your picture you show 2 vices,so you make step jaws as long as your part,your jaws are then bolted to just one vice and the 2nd pinches the jaws. This way your stock is held the entier length and can be changed in and out quickly. However this does only work if you stock is straight to start with, (within reason).Just a thought

[Cmailco]

What are your requirements for flatness and finish?

[Ydna]

I doubt this would work in your situation but you might also give some thought to a vacuum vice system. Last year I made a little setup with a few vacuum venturis that was used to hold down some small aluminum and brass coupons. I wasn't doing much to them, just dusting off the top to rid the stock markings (single tooth flycutter) then engraved. Only went a couple thou deep, but enough that the finish was worthy.
Your parts probably require too much work for that to apply, and probably wouldn't be justified doing a whole new setup just for the facemill operation, but I thought I'd throw it out there anyway...

[hitachibos]

if your need 1000 pcs, do you have a friend in a sheet metal shop? have them run them through a timesaver. 4-5 passes should get you to size.

[peter.blais]

Well, the issue isn't really tolerance so much as finish. Those plates shown make 4 parts each- so each part is small enough it's not difficult to hold a reasonable tolerance across the part. On the parts I used to farm out, we would specifiy like +/- .003" thickness and then the two faces parallel .0015 on a small part- in short, fairly forgiving stuff.

As far as finish goes, these are our own brand / marketed parts- and while really any old finish would work in this application, functionally, we try to only put out parts which are very appealing especially after anodizing.

In the past, I've had shops do thin parts like this for us which I'm pretty sure they simply hit on a belt sander after machining. It looked like they used a very fine belt to just give it a brushed look. That looks great as well, but I don't treasure the thought of doing it in much quantity. The parts I've got coming which are the big quantity job are only like 1" x 2" x .230"- sounds like a lot of skinned fingers.

On the thicker parts, I try to face mill them to a very fine finish so that no finish work is required- just drop them in a box and send to anodizing. That's what I was shooting for here, but not sure that it'll happen.

Perhaps I should look into a vacuum fixture of some sort for doing the facing. It would probably give the same finish as using the mitee grip or similar, but without the cleanup / mess of an adhesive type product. If I was smart about it, I could probably use the same fixture for machining my thin stock for most products which use it.

Actually, I just looked at it, and I think I could reasonably easily add some vacuum workholding to this existing fixture. Mill some grooves in the surface leading to a 1/8" NPT or something in the middle, and an O ring groove around the peripheral. Keep the mitee bites on there to stop it sliding around- perhaps reduce their number though and don't torque them very tight.

[peter.blais]

Carpet tape-

For those of you who suggested carpet tape... I did a little searching and Mcmaster has something similar I think. "general purpose polyethylene tape"- says it's good for quickly tacking carpet, among other things.

It says the temp range is up to 120 deg F. Are you guys using heat to release this stuff? Reusing it multiple times, or do I need to peel it up off the fixture every time and replace it?

I'm going to do a vacuum setup I think for my big quantity job i think but I do need to just get this other short run done asap, and that seems like a good option. I could have the tape here tomorrow from grainger or mcmaster.

[Cmailco]

I don't see any real advantage to running the 24" parts in a plate setup with the Mitee Bite clamps, vs doing something similar to what is linked: Two 6" Kurts each fitted with 12x2" soft-jaws, milled such that the under support is maximized. Allows milling the ends to get final length as well, not to mention, the clamping loads are identical (vector) but with greater surface area contact. You wouldn't need much torque.

This is assuming that the width is fine at mill finish, as you haven't mentioned machining along the lengths.

Just throwing ideas out there.

As far as production level work, a vacuum chuck is a good investment for obvious reasons. Production with tape or adhesives means using two tooling plates, one to load while the other is in process. You cannot reuse the tape, so that means cleaning the plate after each run (alcohol or laquer thinner), reapplying tape and getting everything seated in place. Small parts work extremely well atop a tooling plate, using a break-out method with .10 web between each peripheral cut. The amount of floor-leave is dependent on the tool diameter used to profile, but it works extremely well as long as you keep the concave side of the material 'up'.

Best regards,
Chuck

[Cmailco]

By the way, one product I've had nothing but good experiences with is Aquabond. It's a water soluble thermoplastic bonding adhesive, which also happens to be eco-friendly. The releasing agent, mixed with hot water is all you need to destroy the bond. Nice product and something I've always kept around the shop as it comes in handy at times.