Boley D-bed Cross Slide Attachment

[systeman]

I've just purchased my first lathe. It's a Boley with a D-bed and loads of accessories. It's one of the accessories I have a question about.

The previous owner had completely unwound the lower slide from its internal anchor nut. It's the nut for the adjuster for the lower bed.

It was easy enough to take it apart and reassemble it, but the thread in the nut needs to be re-tapped because the adjuster spindle is too tight.

Does anyone know the tap size for the thread?

It's a left hand wound thread and 4mm diameter.

Thanks everyone.

[oldhippy]

You need a thread gauge.

[measuretwice]

you've got the 4mm part, now you need to know pitch.   As OH suggests use a thread pitch gauge....or set your caliper for say 20 mm, set one  leg at crest and count the thread crest to the next leg...divide that by 20 and you have your pitch

Its going to correspond the the markings on the graduated collar , so double check against that, that it makes sense.  i.e. if the collar have 50 divisions, and each means an advancement of .01 mm, the thread pitch should be .5.  You can get to the pitch directly that way, just that the collars aren't always clearly marked.

Having said all, I really question re tapping without a lot of careful consideration.  What could have cause this?  Is it tight only when assembled, or will nut not smoothly run on the feed screw when apart?  If it goes on apart but not assembled, its likely an alignment issue.  If won't go on in either case, its likely a damaged male thread.  Internal threads wear and get more loose, not tighter....unless its something catastrophic.  External threads otoh are easily subject to dings and bruises.  If the external is damaged, the last thing you want to do is run it through the nut else you risk damaging the nut....a feed screw is a fine precision element of a machine tool and they must treated with care.

i would start by carefully examining the male thread with a loupe for any imperfections.  With a very fine watch makers file, remove them or if there is a lot of damage, get a die and chase it.  Get a quality adjustable die and do it very carefully - too much and instead of chasing it you remove to much and change the pitch diameter and greatly increase backlash....do any or all of this with the utmost of care

Edited June 23, 2018 by measuretwice

[transporter]

As has been said, grab a pitch gauge and check with that, I had to re it a thread on a pendulum after I had to repair it, then re cut the bob,  result nice new threads that I had chased and when clock ran the bob would make its way down the pendulum, took a couple of days to notice what was causing the time to go awry, solved it by making a tiny nut that sits under the bob acting like a lock nut. So to sum up take care when re threading etc, just incase.

[systeman]

5 hours ago, measuretwice said:

you've got the 4mm part, now you need to know pitch.   As OH suggests use a thread pitch gauge....or set your caliper for say 20 mm, set one  leg at crest and count the thread crest to the next leg...divide that by 20 and you have your pitch

Its going to correspond the the markings on the graduated collar , so double check against that, that it makes sense.  i.e. if the collar have 50 divisions, and each means an advancement of .01 mm, the thread pitch should be .5.  You can get to the pitch directly that way, just that the collars aren't always clearly marked.

Having said all, I really question re tapping without a lot of careful consideration.  What could have cause this?  Is it tight only when assembled, or will nut not smoothly run on the feed screw when apart?  If it goes on apart but not assembled, its likely an alignment issue.  If won't go on in either case, its likely a damaged male thread.  Internal threads wear and get more loose, not tighter....unless its something catastrophic.  External threads otoh are easily subject to dings and bruises.  If the external is damaged, the last thing you want to do is run it through the nut else you risk damaging the nut....a feed screw is a fine precision element of a machine tool and they must treated with care.

i would start by carefully examining the male thread with a loupe for any imperfections.  With a very fine watch makers file, remove them or if there is a lot of damage, get a die and chase it.  Get a quality adjustable die and do it very carefully - too much and instead of chasing it you remove to much and change the pitch diameter and greatly increase backlash....do any or all of this with the utmost of care

Thanks for all the input guys.

The adjuster thread is good. The nut though was slightly damaged so needs to be re-tapped because it's too tight.

Knowing the type of thread would be good prior to working out the pitch. Does anyone know if Boley used the metric system?

I've feeling I'll need to arm myself with  several gauges of different types.

[measuretwice]

20 minutes ago, systeman said:

Knowing the type of thread would be good prior to working out the pitch. Does anyone know if Boley used the metric system?

I've feeling I'll need to arm myself with  several gauges of different types.

They're German so the answer is yes...whether they ever used an imperial thread is doubtful but its also impossible to say that it never happened.  Dollars to to donuts its metric.

do you have a caliper?  even a good rule.  Start as I described by counting crest over a known distance and compare that to the graduated dial, there should be an obvious match

Edited June 23, 2018 by measuretwice