Threading on boxford CUD

[Sean64]

I tried a m12 1.75 which worked perfectish. And I did use a live centre to support it

 

[Sean64]

Just to check, you're not bringing your compound out on every cut are you? You are only put cut on with the compound?

I've been calling the cross-slide the topslide ....sorry for the confusion ,my bad

 

[Sean64]

I can't see anything wrong with your setup, but could you elaborate on this. I believe the compound and top slide are just different names for the same thing.

Sorry Richard ,of course I meant "cross slide " not topslide !!

 

[Brad93]

I bet the 1.25 thread doesn't work with the thread dial.

See my lathe you can't do a 1.75 thread with the dial. You have to keep the half nuts engaged. I've got a 4mm pitch lead screw. You've got a 3mm pitch. I bet you can't do 1.25mm threads

 

[Sean64]

I bet the 1.25 thread doesn't work with the thread dial.

See my lathe you can't do a 1.75 thread with the dial. You have to keep the half nuts engaged. I've got a 4mm pitch lead screw. You've got a 3mm pitch. I bet you can't do 1.25mm threads

You're maybe right..... There was a guy on FB said the same ... strange how it will cut 1.5,1.75 but not 1.25 .

Sean

 

[Brad93]

You're maybe right..... There was a guy on FB said the same ... strange how it will cut 1.5,1.75 but not 1.25 .

Sean

It's to do with the pitch of the lead screw and the gearing. There will be pitches that can't work out with your 20T or 21T dial thread indicator.

 

[Brad93]

You just need to keep your half nuts engaged

 

[fizzy]

You just need to keep your half nuts engaged

I have yet to try threading but on a Colchester I think you need to keep it engaged and reverse the motor each time for a metric thread. Possibly the same here.

 

[daedalusminos]

Does your thread indicator have two gears as implied by @Pete. photo?

 

[Sean64]

Does your thread indicator have two gears as implied by @Pete. photo?

Yes , a 20t and a 21t

 

[daedalusminos]

Yes , a 20t and a 21t

Which do you have engaged - Pete's chart says 20T for 1.25mm and 21T for 1.75mm

 

[Martin-Sy]

This is very strange!
Boxfords own chart (post #5 by Pete) says it should work and to engage the 1/2 nuts on A or C.

It looks like there's a 'C' at 90 deg and 180 deg. With 20T driving the indicator 5 revs or 10 revs of the leadscrew.
The carriage would move 5x3 = 15mm (first C) or 10x3 = 30mm (second C) or 20x3 = 60mm (back to A) ALL of which are exactly divisible by 1.25mm so the thread should line up.

Are you sure you've got the 20T driving the dial?

 

[RobCox]

If you have a 3mm pitch leadscrew and a 20T pinion on the threading dial, one rev of the threading dial is equivalent to the leadscrew making an effective travel of 60mm, which divides by 1.25mm to leave an integer, ie a whole number of thread pitches, so it should re-engage synchronised up with your 1.25mm thread.
Doing the same maths for a 21T gear gives an effective travel of 63mm, which is an integral number of 1.75mm pitches, but would be offset by 0.4 thread pitches for a 1.25mm pitch.
I'm sure you've checked, but it does seem plausible that the 21T was engaged on the leadscrew for a 1.25mm pitch.

Edit - looks like @Martin-Sy beat me to it!

 

[Sean64]

Which do you have engaged - Pete's chart says 20T for 1.25mm and 21T for 1.75mm

Because I just cut the 1.75 pitch m12 I have the 21 /position 2

 

[daedalusminos]

I would verify your thread indicator - select position 1 and with the leadscrew stationary, move the saddle for 1 revolution of the thread indicator and measure distance travelled by the saddle. Repeat for position 2.

 

[Misterg]

The threading dial I know nothing about it so will have to research on this

My apologies for possibly insulting your intelligence, but the threading indicator is spinning when the half nuts are disengaged, isn’t it? (I don’t know the lathe, so don’t know if it is possible for it to be disengaged.)

The 3mm pitch leadscrew will be in synch with a 1,25mm pitch every 5 turns, so 4 times per revolution if you’ve got the 20T threading indicator gear.

The only other thing I can think of is to make sure that you’re engaging the half nuts well clear of the work to give the carriage a bit of space to settle down before the tool starts cutting.

 

[Sean64]

M6 1.0 turned out perfect

 

[Sean64]

My apologies for possibly insulting your intelligence, but the threading indicator is spinning when the half nuts are disengaged, isn’t it? (I don’t know the lathe, so don’t know if it is possible for it to be disengaged.)

The 3mm pitch leadscrew will be in synch with a 1,25mm pitch every 5 turns, so 4 times per revolution if you’ve got the 20T threading indicator gear.

The only other thing I can think of is to make sure that you’re engaging the half nuts well clear of the work to give the carriage a bit of space to settle down before the tool starts cutting.

I was tight for space because of the live centre being in the way,your point about starting away from the piece makes sense .

Sean

 

[Misterg]

M6 1.0 turned out perfect

A 1mm pitch will be in synch with a 3mm leadscrew every turn (of the leadscrew) so wherever you engage the half nuts will be OK - still points to something related to the threading indicator giving a problem with the 1,25mm pitch IMHO.

 

[Pete.]

A 1mm pitch will be in synch with a 3mm leadscrew every turn (of the leadscrew) so wherever you engage the half nuts will be OK - still points to something related to the threading indicator giving a problem with the 1,25mm pitch IMHO.

That is correct and it applies to ANY pitch that is achieved by dividing the leadscrew pitch by a whole number.

So for a 3mm pitch screw:

3/1=3mm
3/2=1.5mm
3/3=1mm
3/4=0.75mm
3/5=0.6mm
3/6=0.5mm
etc...

All of those can be engaged anywhere and will always synchronise.