Lathe Re-Chucking
Lathe Re-Chucking
(OP)
I have a part here with an accurate shaft for pre-loaded spindle bearings, and an inside diameter on the opposite face from the shaft, for mounting a hub. The part must be machined in the lathe, then re-chucked to do the opposite feature. I am using the shaft as my datum, and I have applied a positional tolerance of Ø0.05mm on the inside diameter. It appears that our machine shop used every bit of this. This particular shop is fast and cheap.
How accurately can a shop centre a part in a lathe, when they re-check to a datum feature?
How accurately can a shop centre a part in a lathe, when they re-check to a datum feature?
--
JHG
RE: Lathe Re-Chucking
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
RE: Lathe Re-Chucking
+/- 0.001 is routinely achieved for centerline accuracy and part diameters; 1/10 of 1/1000 can be met if you need it. Lathe accuracy (tool rigidity, bed accuracy, gear and runout problems sometimes are more limiting than initial positioning. The machinists I work with often find that a 4-clamp lathe is often more accurate (but slower) to dial in than a default 3-clamp head.
But, accurate, fast, or cheap. Pick two of the three.
RE: Lathe Re-Chucking
If your machine shop is using every bit of the tolerance you have, it is quite possible that they are choosing the /fastest/ tools that will get the job done. If you tighten that tolerance, it may force them to switch to a 4-jaw chuck that requires 'dialing in' periodically, or possibly for each part, and your cost/part will increase.
Then again, are your parts working? Is there excessive fail/scrap rates? If not, why care? If so, then yea, look at how much your tolerance needs to be to still function, and open it as much as you can tolerate.
RE: Lathe Re-Chucking
My part is a one-off assembly fixture. The mating part will be manufactured in the hundreds (we hope). I am considering sending my piece out to a better quality shop. I am not sure why it did not got there in the first place. In addition to my specified positional error, I have a couple of assembly clearances to sort out, so this is quite a bit more than operating a lathe.
Thanks everyone.
--
JHG
RE: Lathe Re-Chucking
A standard three draw chuck should hold a component concentric to about 0.003" after it's been turned around.
Using a four jaw chuck and setting up correctly should enable you to get within about 0.001" for the same procedure.
“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein
RE: Lathe Re-Chucking
The catalog tolerances for diameters and concentricity and shoulder abutment perpendicularity and runout for spindle bearings are WAY tighter than 0.05 mm.
How did the shaft shop do on those,and what did you ask for?
RE: Lathe Re-Chucking
The spindle bearings are off-the-shelf. They are angular contact. The front faces are lapped such that when you compress them together, they preload. I installed these, not the shop. I should inspect the mounting shaft. The assembly is sitting here and I can feel no clearance. I called up an accurate tolerance. I believe most of my runout is centration between the shaft and the bore on the opposite side.
--
JHG
RE: Lathe Re-Chucking
http://products.emersonbearing.com/Asset/barden_co...
RE: Lathe Re-Chucking
My bearing attachment is very accurate. My problem is a pocket on the opposite side of the part, that we mount stuff into. The bearing appears to be working fine.
--
JHG
RE: Lathe Re-Chucking
Mike Halloran
Pembroke Pines, FL, USA