Problem- Chuck's Taking Bites and Ruining My Finish

[JWB_Machining]

Ok. So i have to to make compression test samples which should be really easy. I'm making them out of 6061 Alumium 1" Diam Round stock. I just have to turn down the stock and face both ends so I get a 2:1 Length to Diameter Cylinder with as nice a finish as possible. So I turn down the stock to get a nice finish and then I face one end. When I do this I get a Burr but I've just been using high grit sand paper to take that off, any advice on machining it so there is no burr would be great. So now I have to flip the part around, part off the non turned down length, face and deburr the other end. However I've been hit or miss all day as to wether or not my I''ve tightened my chuck enough without leaving bite marks in my pretty surface finish. According to specifications my finish needs to be 63 micro (Mu) inch or better. If I just barely tighten it so as not too leave marks I end up being too light and pushing my part in when I try to face it.

So Basically Is there any way to reduce the possibility of bite marks without causing the piece to be pushed into my chuck when I face it because it's too loose. I'm thinking that this might actually have to come down to experimentation and a torque wrench but if anyone has any tricks I'd be very happy to learn them. I told myself just wrap the part in one layer of paper towel, but then I processed that thought and remained without a solution.

[HuFlungDung]

Use a collet chuck. One option is to use a 5C collet block, you might have seen those kits with a square and a hex block in them. These are designed for chucking in a 3 or 4 jaw chuck. However, the chuck needs to be in good condition, meaning the jaws need to be snug and ground so that they will hold the block nice and square to the chuck face.

[Geof]

Two ways:

One is to machine soft jaws to the correct size to grip the parts. Have you had any experience making soft jaws?

Another is to make a split sleeve for the part. Depending on how many you are doing the sleeve can be more efficient because you can have a flange around the OD so it comes up against the jaws, and a flange at the bottom of the ID so the part bottoms out. This way you push the parts in to the same position and they can be faced to length.

Regarding your burr figure out how to put on a chamfer; althoug a significant burr suggests your tool is dull or maybe above center and rubbing.

[JWB_Machining]

Wow i'm an idiot for not thinking to use a Collet, I guess that's what happens when you have only been machining 8 months, you don't always think of these things (And Just Today I was telling myself how Proud I was of myself for my ability to get around a bunch of machining problems) . My boss has bought plenty of collets i'll have to mull through those tomorrow morning and find something. Does anyone know off Hand if my Chucks for my 1950's pratt n Whitney lathe fit in my Haas TL-1 or is it a different style? i've still never taken the Chuck off the TL-1, It's just been there since they hired me.

Geoff I've only machined soft jaws for my 4" vise, never for a chuck, I feel There's no way I would be centered with my lack of experience. A Split sleeve seems like a real good idea but i'm only making 15, and I think i've got 6 that I can pass as acceptable as is.

In regards to my burr it's not really pronounced or anything just take a few seconds of sanding. IPS on my Haas TL-1 makes Chamfers easy enough but what do you think is better to do? A Few seconds of high grit sanding till my finger tells me it's smooth or the chamfer?

Thanks for all the help again guys. I still can't believe I didn't think to use a collet.

[Geof]

Originally Posted by JWB_Machining ...Geoff I've only machined soft jaws for my 4" vise, never for a chuck, I feel There's no way I would be centered with my lack of experience.....

There have been several threads on machining chuck jaws; it is impossible to have them off-center because you machine them in the chuck. Do a bit of a search, I think some threads were in the Haas lathe forum.

You need to get up to speed on writing simple facing programs with chamfers included they will remove the chance that you put a slice in the end of your finger when the sand paper slips.

Remind me some time and I will post examples of what I call my template programs.

[mrcodewiz]

I agree on the collet for 1". That is the max diameter I can do in a collet on my lathe - if it is more than that, I use the 3 or 4 jaw and wrap the work with a piece of aluminum cut out of a beer can. This generally allows me to tighten the chuck without damaging the part.