Learning milling the hard way

[DPittman]

I knew the piece wasn't perfectly square cuz I welded it up....and I knew the clamping force couldn't be exactly the same on both sides of the vice but I still figured it would be ok. I figured wrong.

Busted the end mill and as you can see the piece worked out of the vise and then crawled up the side of the end mill.

Lesson learned so far... better work securing and I think climb milling exasperated my problem.

I just wanted to mill a couple of parallel slots/channels in the sides of this box.

 

[YYCHM]

Ya.... tell me about it. I toasted a 1/2" 2 flt yesterday trying to mill two 1-1/4" dia by 3/8" thick washers to the same thickness at the same time. Pulled out of the vise on the final pass. Blaaaaaa!!!!!

The two washers were cut from the same stock so I thought the vise should be able to grip them both.

 

[PeterT]

We have all been there. I think its good to post things that didn't work out. Not to be critical of ourselves others, but to show the scenario to avoid problems 'next time'.

Aluminum can be challenging. Because its a bit softer alloy, a flute entering the cut the wrong way can dig in. Then once things start to deflect (the part, the end mill, the clamping arrangement) it can feed on itself getting progressively worse & end with a bang. It can also be gummy which smears on the tool, degrades the cutting edge, more heat, more friction, more local expansion... Materials like copper can be even worse.

Thin walled parts can be extra challenging. There is less mass so by default less rigidity & more chance of flex during machining. So generally need to reduce in-feed (smaller chips). Its amazingly easy to destroy thin walled parts like ordinary tubing just cutting them with a saw if the teeth are too coarse. In your case maybe a smaller EM or peck plunging the notch vs tying to mill through it from the side? hard to say. One hack I have done is 5-min epoxy in a sacrificial block of scrap wood to give the thin walled part stability during cutting. Then just heat the adhesive with a heat gun & the block comes out pretty clean.

I generally avoid climb milling unless its a finishing pass & low DOC. Even so, always good practice to lock the carriage. But problems can still happen with a tight machine ways if the part is not secure. This can happen in the vise - clamping pressure slightly deforms thin walled objects. So it doesn't take much micro deformation at all & you to could end up at say 25% contact area vs 100%, so that means proportionately less grip. Sometimes a thin piece of cardboard like a business card helps distribute the jaw grip but its not a perfect solution.

I've had some blowouts trying to machine multiple (so called identical) parts in the vise. I've watched some vids where machinist will put aluminum TIG welding rod on the moving jaw side to make up the part width discrepancy. The only issue is, you are left with a very tiny clamping surface area (the tangent edge of the circular cross section). It works, but the parts had better be quite rigid & stiff on their own. And the wire should be high in the jaw so the vise pressure is pushing the part slightly down into the vise parallels. What I found works better is solder because it is very malleable & deforms & adapts to the parts. But its not really a multiple use thing once squished & not exactly throwaway cheap.

 

[Tom Kitta]

The problem with us is that we usually work with variety of strange parts that are one off. Thus having accidents with unknown material happens.

For iffy stuff I usually try to use HSS - its ultra cheap and resistant to abuse. Also using smaller EM as mentioned can help.

 

[DPittman]

Thanks for the tips.

I did put in a chunk of soft aluminum bar and I think that helped but I'm also a bit gun shy now so I am taking it easy.

Maybe there is a much better way to accomplish this? I want to get to about 1" depth.View attachment 11037View attachment 11038View attachment 11037View attachment 11038

 

[Dabbler]

... so you want a 3/4" wide by 1" deep slot in the middle of a square aluminum tube?

this is what machinist's jacks help with, and using them to tighten against the jaw pressure is one way of holding the thing in place....
'
I've milled all kinds of tubing sections, and milling square sections in that orientation is a pretty advanced activity. It just looks simple...

Using your hold down set to clamp the non-milled sides down will help a lot also.

 

[DPittman]

... so you want a 3/4" wide by 1" deep slot in the middle of a square aluminum tube?

this is what machinist's jacks help with, and using them to tighten against the jaw pressure is one way of holding the thing in place....
'
I've milled all kinds of tubing sections, and milling square sections in that orientation is a pretty advanced activity. It just looks simple...

Using your hold down set to clamp the non-milled sides down will help a lot also.

It was steel not aluminum and I got it done....probably not the right way but I got it with out any more breakage or bodily harm so thats usually considered a success in my shop.

 

[Dabbler]

There's no 'right way' You got it done - and that's just fine! - sorry about the aluminum; I misread the posts!

 

[Tom O]

Try sticking it down with crazy glue I’ve found it works good. There are some good vids of it on nyc Cnc.
PS, sent it to PT to sit with his scream artwork!

 

[DPittman]

Try sticking it down with crazy glue I’ve found it works good. There are some good vids of it on nyc Cnc.
PS, sent it to PT to sit with his scream artwork!

Hmmn I don't think crazy glue would help much in this instance.

 

[Tom O]

Hmmn I don't think crazy glue would help much in this instance.

That was more for YYC’s benefit.

 

[YYCHM]

That was more for YYC’s benefit.

Glue what to what LOL.

I was attempting to mill two pieces like this to the same height

 

[PeterT]

Yup, one can almost feel the bang coming, LOL.

2 parts simultaneously is not doing the setup any favors because if one diameter is different than the other, even by a thou, that means the smaller diameter is not being clamped with the same force (if much at all). It can only be clamped by squash/distorting the bigger one. Now in reality vise jaws have some give, but its not something you should count on. So one part a time would be better.

A vee block on either vise jaw would provide 4 points of contact vs only 2 with just the vise jaw. You could put a fat parallel in between the blocks for more base contact area = more stability. Also the cutting forces are more likely to be directed into the face of the Vee vs spinning the disc against the jaw tangentially where there is little actual resistance.

This is just begging for a clamping fixture with 2 half round openings. Of course that's typically the machinist rub - takes longer to make a special fixture than the part itself.

In simple 'washer making' facing ops like this, you can use the crazy glue trick, but its much easier to do on lathe. Machine a face of a sacrificial scrap. Glue the part on. Take light facing cuts. the single point cutting force is much smaller than interrupted milling cut. Now the adhesive is acting in shear which is typically where they are strongest.

 

[Tom O]

Glue what to what LOL.

View attachment 11040

I was attempting to mill two pieces like this to the same height

Well you could turn a rod down to hold it from the center then glue/press fit them together.