accurate length of lathe parts..

Home Model Engine Machinist Forum

Help Support Home Model Engine Machinist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

AllThumbs

Well-Known Member
Joined
Jan 17, 2008
Messages
213
Reaction score
1
Since we can't measure parts while in the chuck, I was wondering how best make parts to the correct length.

The way I do it is make the part, part it off a little long. Chuck the part, clean up the face. Remove from chuck and measure. Make a mental note of how much needs to come off, rechuck. With the lathe off, touch off the face with the tool. Zero the dro, and take cuts until I have removed the correct amount. This gets me to +/- .005, which may of may not be close enough.

What is a better way?

Eric
 
Most of the time I do what you describe.

Assuming the back face (the face facing the chuck) has been faced...

If the back face is against the chuck face, use a depth mike to measure from the front face to the chuck face = part length.

If the back face is forward of the chuck face, put an adjustable parallel between chuck face and back face of part, then use depth mike to measure from front face to parallel.

If the part projects back into the spindle, you're on your own. I have no good suggestions.
 
Sometimes it may be convenient not to have to remove and reverse the part in the chuck. You can make a trial cut with the parting tool just deep enough to measure where you are and work from that. This assumes you aren't too picky about the parted off finish or exact length and don't need to face and clean up that side to precision. I find that's often true.

Best,

BW
 
Eric
On the CNC lathe that I operate at work we usually have multiple piece orders to run.
OAL tolerances are often to a +/- .002"
For that first part we set a stop for the finished face to rest on, dust the raw end and
pull it out to mic the length. We teach the "Z" offest to bring the length to tolerance and
stick the part back in the chuck against the stop.

It will run 20 pieces and hold that +/- .002" tolerance.

If anyone comes up with a better way than what you are already doing, I'm sure the
manufacturing machine shops around the world would be happy to pay for the idea! ;)

Rick
 
Rick that is the same way we do it at work. As long as everything can be kept consistant you can hold the length very close. I remember ,when I started machining,
learning that the diameter you are chucking on when using collets plays an important role in your OAL. I you are facing your parts in a 5C collet using a stop in the collet and your parts OD varies so will your over all length. I don't remember the ratio I was told but I recall that a .002" change in our diameter made us have a hard time holding the OAL tolerance. We started using dead length collets after this and with those the OD being chucked is not near as critical.
 
Eric, here is a quote from my thread on making the cylinder for the engine I am building now.

"face the band saw cut end, remove and measure length, replace back in the collet chuck then face off to final length."

It's the only way I do it when I need to be some what accurate. The part needed to be 2.5" and I ended up at 2.498". Could have been worse...:))
 
most of time as you describe, other way if you need a bit more accuracy or have many to do is a collet or a chuck stop - a useful hsm project. clamp carriage, compound at 90 (or micrometer carriage stop), take a cut, remove work, measure and when you replace its in the same position.
 
HI
Same way, face off both ends allowing a little over the finished length mic the overall length.
Bring the tool up to the face of the work zero the compound slide dial. Wind on the compound slide the amount that needs removing after locking the saddle and bringing the tool out, and then face off.
remove the work and remeasure. Should be able to hit +- .001 with out too much trouble.

Most important thing is only measure over machined faces and not a bandsaw cut face.

Cheers kevin
 

Latest posts

Back
Top