Thread: Runouts on machinery

Bob,

After the playtime with the Sherline I screwed the 80mm PB Griptru onto the spindle. The fun stopped there. The chuck utilises three tangentially mounted tapered screws to provide concentric adjustment. PB reckon that accurate adjustment can be made within one minute. I obviously need practise but after considerable rooting around I managed to having it running with a repeatable, just under 0.01mm TIR IF I used the key in the same socket. Wrong socket and it was all over the shop. The 5" TOS 3 jaw favours one socket and it's not the factory marked favourite.

Are you mindful of which socket you are using?

Bob.

Originally Posted by Anorak Bob

The 5" TOS 3 jaw favours one socket and it's not the factory marked favourite.

Are you mindful of which socket you are using?

Bob.

Nope - something else to check.

I tried AB's suggestion of moving the MT arbor around in the socket and measuring the RO

For the first test I decided to use my worst chuck - the keyed chuck that came with the DP, but I did the measurement in the lathe because the DP has a tanged spindle and only provides for two positions of the MT3 arbor.

The next problem is the keyed chuck is an MT2 so it needs an adapter to hold it in the lathe. The adapter is also a tang fit so I can only rotate the MT2 Chuck by 180º in it teh MT2/3 adapater.

I measured the RO at 4 positions separated by a 90º movement of the MT3 (first number in mm) and then rotated the MT2 and repeated the 4 x 90º MT3 rotations again (second number)

Position 1: 0.49 , 0.51
Position 2: 0.39 , 0.49
Position 3: 0.51 , 0.45
Position 4: 0.51 , 0.45
So clearly there is better socket and arbor relationship than others - not that any of them are anything to rave about.

Next I tried my best MT3 keyless chuck in the DP. Because its tanged it only has 2 positions.
Position 1 was 0.045 and position 2 was 0.025 - well worth doing and checking - it should be easy enough to mark the chuck and spindle to keep using the better position.

Next I tried the 4" 3jaw on the lathe and used different chuck socket holes to tighten the bit onto the chuck.
After doing a measurement I removed the bit and turned the scroll by 180º before retightening the bit using a different socket.

First number refers to socket hole and second number is RO in mm.
1: 0.09
2: 0.11
3: 0.03
So a very significant difference - I have marked that hole with a punch character "C" for chuck key.

I find it a *lot* easier and less brain-strain to just accept that 3 jaw chucks are convenience tools for turning you're going to do in a single setup using slightly oversized stock. Then the runout is irrelevant.

If I want accuracy on an already machined surface I use a collet or a 4 jaw chuck. My P-B collet chuck gets a lot of use because the collet range goes from 3mm to 40mm in 3mm steps. I might have a 1.5-3mm collet too.

This business of finding the 'right' socket to tighten the 3-jaw chuck - give me a break! I use all the sockets.

I'm *far* more interested in how much taper I'm getting on a shaft. Currently the Chipmaster is down at the 0.0003" in 8" range after I tweaked the headstock a bit.

PDW

Here is my mill with 100mm Y between rows. I used my cheapest DTI and not the most rigid setup as I wasn't expecting it to be that close. If I can find a gauge block I might just have another go with a better setup.