Boley cross slide indicator and backlash questions

[JonasB]

Hello everyone, I recently picked up my first G Boley 8mm D bed style lathe and I have a couple of questions. I disassembled the headstock and cross slide as the lathe hasn’t been running for past few years and I wanted to give it a good start. Everything went smooth and after tightening the conical bushings, the lathe has barely any runoff ~0.001”.

One thing I noticed when I disassembled the cross slide was that the thread feeding the cross feed had been damaged, see first photo. I suspect this may have at some point used/replaced the screw which holds the feed nut with one that was too long and pressing onto the thread when tightened. So obviously when someone ran the feed, the thread got damaged. I shortened the screw as it was indeed hitting the thread if screwed in all the way, but the damage was done. So my first question is, does anyone have any of these thread axises laying around or would know of a good alternative to fix this? As a result, the feed is a bit janky and there is about 0.2mm of backlash (I can live with this)

 

My second question is about the actual feed indicator, I see the feed is indicated in 1/12 steps or maybe 1/12.5?. Does this mean that each step is 1/12 of a mm? I ran the cross slide with a dial indicator (0.0001” accuracy) setup and measured a few turns and it seems to confirm that (mean measure was around 0.0034”). so maybe more of a history question, but why would someone use that scale vs 1/10mm? Last step to verify could be to run the lathe and just measure a piece, but I dont have a graver that would fit the slide just yet

Posting that dial setup in the last photo below, I dont have a depth gauge I could setup, so there is some cosine error, but I assume we can safely discard this at this small of a travel distance?

Anyways, sorry for the lengthy post, I love the lathe and looking forward to using it, happy holidays everyone!

[praezis]

Hi

it looks like there are 15 dvisions on the drum. Then 1 equals 1/15 of the screw pitch, of course.

I don‘t know what you try to measure with your shown setup?

Frank

[JonasB]

42 minutes ago, praezis said:

Hi

it looks like there are 15 dvisions on the drum. Then 1 equals 1/15 of the screw pitch, of course.

I don‘t know what you try to measure with your shown setup?

Frank

Where do you see 15 or how did you get to that number? That drum indicator shows 12

[Klassiker]

18 hours ago, JonasB said:

Where do you see 15

I see 15 too. 12 (marked) plus 3 (unmarked) to get back to zero (marked).

[nickelsilver]

Yes, as above, 12, then 13, then 14, then 15 (which is 0). That would suggest 1.5mm pitch screws, but I have a feeling they aren't that coarse; are both drums the same? I have seen old lathes with 0.75mm pitch screws, if that's your case, this drum would be for the feed on the work diameter, the idea being it's direct reading.

 

The likelihood of finding a new or used screw for one of these is very small, best would be to check for burrs on the damaged part and clean them up and use it as is. Note that there is an adjustment for freedom at the screw bearing, in the drum assembly. Often what's taken for backlash in the screw is actually play there.

 

Your indicator setup needs some work. The indicator tip should be at an angle of around 12 degrees to get an accurate reading; in the pic it's almost perpendicular to the piece being measured.

 

 

[JonasB]

2 hours ago, Klassiker said:

I see 15 too. 12 (marked) plus 3 (unmarked) to get back to zero (marked).

Oh yes of course, now I feel stupid

1 hour ago, nickelsilver said:

Yes, as above, 12, then 13, then 14, then 15 (which is 0). That would suggest 1.5mm pitch screws, but I have a feeling they aren't that coarse; are both drums the same? I have seen old lathes with 0.75mm pitch screws, if that's your case, this drum would be for the feed on the work diameter, the idea being it's direct reading.

 

The likelihood of finding a new or used screw for one of these is very small, best would be to check for burrs on the damaged part and clean them up and use it as is. Note that there is an adjustment for freedom at the screw bearing, in the drum assembly. Often what's taken for backlash in the screw is actually play there.

 

Your indicator setup needs some work. The indicator tip should be at an angle of around 12 degrees to get an accurate reading; in the pic it's almost perpendicular to the piece being measured.

 

 

Thank you so much, I will remove the screw and check the pitch, but that seems to match with my readings!

[praezis]

22 hours ago, JonasB said:

Oh yes of course, now I feel stupid

Not your fault - we all were equipped with 10 fingers only, hard to count up to 15 then 

23 hours ago, nickelsilver said:

The indicator tip should be at an angle of around 12 degrees to get an accurate reading;

That is new to me. I was convinced, you will get the least error if the movement is exactly perpendicular to the bolt.

Frank