Maintaining parallelism when facing both ends of a part

davidpbest said:
Are you using a chuck stop when seating the part for the second op? By "chuck stop" I'm referring to this type of setup:

View attachment 436844

I have a setup like that, and simply zero out the DRO against the face of the stop. But for really tight tolerance work, I also made a set of adjustable chuck stops that mount directly to the chuck. I documented that effort in this posting:

www.hobby-machinist.com

Adjustable Chuck Stops For 3 and 4 Jaw Chucks - long post

This is not specific to Precision Matthews, so if this post belongs somewhere else on this site, let me know. I decided I needed useful chuck stops for my PM1340 lathe. I had tired of trying to use a pair of parallels to hold stock off the face of a chuck in bringing the stock to an...
www.hobby-machinist.com www.hobby-machinist.com
Click to expand...

I don't, but I know I've needed one several times. I used a set of cheap parallels to set the part depth. Not sure if that helped or hurt me.
 
If I needed it to be perfect I'd make a sacrificial expanding mandrel.

Turn all the parts just a bit over length.

Turn the mandrel to size and do not remove it until the job is complete.

Make sure you can face both ends in the same setup so the mandrel will need to stick out just far enough to sneek a left hand tool in to face the chuck side face.
 
dbb-the-bruce said:
Without seeing the other end of the part....

Face both ends in a single mounting operation (not complexity) Start with a piece about 1.5 to 2 time longer, and turn the cylinder you want leaving enough to work with. You end up with the cylinder and two shoulders to waste shafts on each end. The point being that if cross slide / lathe is setup good you have a constant diameter cylinder and two parallel faces because the part was spinning on exactly one axis. Then it's just a matter of picking up those reference surfaces and indicating them when you remount to work the end details.

Hope that's clear enough. Use the precision that's baked into your lathe.
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I think I understand. But I need one shoulder to hold the part? How would I put it on a mandrel and be able to turn both faces?
 
LVLAaron said:
No problem making a mandrel. Part is threaded so it's pretty easy to set up. The thread fit isn't even that important.. they have some slop by design.
So... I'd turn the threaded mandrel in situ... thread the part on... one face is tight against the mandrel... turn the inboard face. Sounds easy enough.
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Don't thread the part on.....expanding mandrel that lines up the part by the bore. Threads aren't accurate.
 
If you don't mind cutting some slight grooves into the mandrel you could use one of these for the final facing of both ends. It will get you pretty much dead perfect.

www.ebay.com

#6 (1 to 1-1/4) Expanding Mandrel | eBay

Hardened and precision-ground. Consists of tapered arbor and expanding sleeve (s). Any size within the range may be obtained by moving sleeve along arbor. Length of Arbor: 9. Range: 1 to 1-1/4. Length of Sleeve: 4.
www.ebay.com

https://www.ebay.com/itm/3517817383...I3B3TI3SPu&var=&widget_ver=artemis&media=COPY
 
Batmanacw said:
If you don't mind cutting some slight grooves into the mandrel you could use one of these for the final facing of both ends. It will get you pretty much dead perfect.

www.ebay.com

#6 (1 to 1-1/4) Expanding Mandrel | eBay

Hardened and precision-ground. Consists of tapered arbor and expanding sleeve (s). Any size within the range may be obtained by moving sleeve along arbor. Length of Arbor: 9. Range: 1 to 1-1/4. Length of Sleeve: 4.
www.ebay.com

https://www.ebay.com/itm/3517817383...I3B3TI3SPu&var=&widget_ver=artemis&media=COPY
Click to expand...
Since you have 2-piece jaws, soft jaws would seem like a lot simpler approach to me.

monsterjaws.com

6" Aluminum American Standard Tongue & Groove Jaws Jaws (3" HT)

TGO612-3A
monsterjaws.com monsterjaws.com

or

monsterjaws.com

6" Aluminum Full Grip Round Jaws for B-206 Chucks (1.5" HT, 6" Pie diameter)

FGB206-15A Chuck Jaws Machinable Aluminum and Steel Soft Jaws softjaws Clamping
monsterjaws.com monsterjaws.com
 
I make them in one position in a 3 jaw chuck. Leave the length you need outside the chuck. Turn the OD and after first cut, the OD is true to spindle. Drill, bore, then thread ID (I thread away from chuck). Since your using it to measure a barrel tenon, you'll want to bore the end opposite the threads a little larger ID, so a depth mic will work easier. Use a cut-off tool and set the end even with the end of the part. Move DRO in until you have the length you want and part it off. Should be perfect lenght. You can either debur by hand or put back in chuck and dial in until no runout on end of part and debur.

If you can't complete all cuts in a single positioning and need to flip around in another chuck, you need a chuck you can dial the part back in to 0. Might be a 4 jaw, or if your 6 jaw is a set true, then Robert is your Mothers Brother.
 
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That's prolly the most easy. Bar in chuck, cut both faces. Deal with the internal features last. I got this
 
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