securing 8 inch pump on lathe - what am i doing wrong?

Savedbygrace77

Aluminum

Joined

Jul 15, 2018

• Oct 14, 2021

• #1

Hi all - so I have a pump from my automatic transmission im trying to cut, its aluminum. I have a nice bit that leaves a very smooth surface but it is a very interrupted cut -

Issue is when I get to the mid/outer section i think the interruption is throwing off the centering which takes me a while to get right (under 1 thou) and makes the bit dig

How can I attach this darn thing so it wont move on the chuck? Im only taking about 5-8 thou at a time, tried med and slow speed on the pulleys..

 

johnoder

Diamond

Joined

Jul 16, 2004

Location

Houston, TX USA

• Oct 14, 2021

• #2

You need a fixture / fixtures - face plate-like

Show us the back - maybe we can suggest what to attach to.

May even result in a fixture that you mount the item on before you screw the fixture on the spindle nose

Hint - a hard wood fixture (or "attaching piece") with lots of contact area will help deaden things out

 

K

Kevin T

Stainless

Joined

Jan 26, 2019

• Oct 14, 2021

• #3

Also the farther away from center you are the more you may have to deal with the slop in your dovetails etc due to more forces. Are yours adjusted well?

 

G

garyphansen

Titanium

Joined

Feb 9, 2004

Location

Traverse City, MI

• Oct 14, 2021

• #4

I have attached plywood to a face plate and then screwed the work piece to the plywood.

 

I

Illinoyance

Stainless

Joined

Aug 24, 2015

• Oct 14, 2021

• #5

We really need to see what the back of the part looks like. How are you holding the part? 3 jaw, 4 jaw, or faceplate?

 

Gordon Heaton

Titanium

Joined

Feb 19, 2007

Location

St. George, Utah

• Oct 14, 2021

• #6

It appears you are gripping by expanding the jaws inside the part. Is the surface you are gripping machined perfectly straight? Are your jaws sloppy in the tracks? Is the condition of the jaws good? And, are you facing the whole casting or just the center section?

My solution is to make a mandrel with a flange, to fit that center hole. Then chuck up in the conventional manner.

 

Savedbygrace77

Aluminum

Joined

Jul 15, 2018

• Oct 14, 2021

• #7

this is the back - all i could do was use the center hole. Had it in a 3 jaw for the facing, then switched to a 4 jaw for the pocket cos its off center.. I should have prob just used the 4 jaw - more clamping force but it is what it is -

 

Attachments

• 
  s-l1600.jpg

  95.2 KB · Views: 44

Gordon Heaton

Titanium

Joined

Feb 19, 2007

Location

St. George, Utah

• Oct 14, 2021

• #8

It would help to see the backside without the shaft, but I think you've identified the problem. Now that you've been cutting on it, is there a known surface left for you to re-indicate if removal from the current setup is required? I believe you're going to have to do that.

 

Savedbygrace77

Aluminum

Joined

Jul 15, 2018

• Oct 14, 2021

• #9

Yes - I made a cut about 80% across the pocket before switching to the 4 jaw and re-indexed off that.. so managed to finish it up with some chatter but was quite a task.. kept trying to grind bits for the aluminum and got very mixed results. Eventually an old bit made a beautiful finish but I couldnt get it into that tight 90 degree corner so just sanded the metal down by hand-

as you can see the finish was pitiful but i was on the last pass and had to use as is... after sanding down it looks fine - nice and smooth..

another issue is I cut into a jacket so not even sure if this is usable as is anymore

 

T

tommy1010

Stainless

Joined

Apr 21, 2010

Location

northeastern Pa, USA

• Oct 14, 2021

• #10

What I see for your cutting bit is HSS with a large round nose. Ugh!! If it was me I would have a very sharp HSS with a very positive rake. It works quite well for aluminum. Remember that the outer diameter of that piece is traveling very fast. With that many interruptions my opinion is sharp is better not a big round nose.

 

Gordon Heaton

Titanium

Joined

Feb 19, 2007

Location

St. George, Utah

• Oct 15, 2021

• #11

Well, shoot! All that work and you punch through at the end. But... unless that hole intersects a casting void you are very thin in other places too, perhaps all the way around. That can be difficult to determine. I would not proceed without addressing that first. You may be able to TIG that hole up and re-machine if it is a 'loner'.

 

SLK001

Stainless

Joined

Feb 8, 2015

Location

Coral Springs, FL USA

• Oct 15, 2021

• #12

My guess is that your interrupted cuts are setting up a vibration in your work that is throwing everything off.