Colchester threading dial

NewGunPlumber · Mar 23, 2020

I have a Colchester master 2500 13" with metric lead screw but unfortunately I'm missing the threading dial so thinking about making one.

Does anyone have a machine the same that would be willing to help out with some info on the gear and number of devisions on the dial?

Any help would be greatly appreciated guys!

johnoder · Mar 23, 2020

SB lathes sold with metric lead screw came with a "four speed" thread dial - and instructions. Wonder how Colchester handled that?

NewGunPlumber · Mar 25, 2020

From what I've seen they have one dial with 4 numbers and 1 additional index mark between those numbers.

I'm not sure how the metric lead screw works but from memory the imperial versions if your cutting and imperial thread you can start on any number. If your cutting a metric thread you need to start in the same number each time

trevj · Mar 25, 2020

NewGunPlumber said:
From what I've seen they have one dial with 4 numbers and 1 additional index mark between those numbers.

I'm not sure how the metric lead screw works but from memory the imperial versions if your cutting and imperial thread you can start on any number. If your cutting a metric thread you need to start in the same number each time

Yer memory is worse than mine.

For inch threads, if you can divide the pitch of the lead screw in to the number of threads, you can engage the half nuts anywhere. Otherwise, about the only safe thing to do is to RTFM. Read The Frikken Manual. Some of the problems come about because of the Odd numbered, or Half numbered threads that are 'Standard'.

For Metrical threads on Metrical machines, same. RTFM.

EPAIII · Mar 25, 2020

I have no information on that lathe, but if you can not find the OEM solution, I can give a stab at designing one that would work. I would need to know the pitch of the lead screw and the exact metric threads that you want to cut. Oh, and if it is an English lead screw, then I would also need to know the ratio of the English-metric conversion gears.

ratbldr427 · Mar 25, 2020

The only metric ones I have seen usen change gears.Imperial screw even threads engage on any line,odd on any number,half on the same no.I think,and when cutting metric don't disengage the half nut.We have an 18x80 Colchester and I think in the manual it shows a change gear dial for metric threads.

SAG 180 · Mar 26, 2020

I've seen a metric leadscrew Master 2500 threading dial recently: they have multiple wheels at different ratios depending on the thread cut. It'll be while before I'm back in that workshop but I'll take some photos.

Hopefuldave · Mar 26, 2020

Metric requires several gears for the thread dial on a metric leadscrew, because metric works as length per thread (lead) not threads per length (TPI), and I've always found it easiest to leave the halfnuts engaged and reverse the lathe when swapping between inch/metric systems - most of the time for native threads too, unless it's a LONG thread.

Dave H. (the other one)

Clive603 · Mar 26, 2020

If you can't find the factory data best alternative is to find a machine with the same pitch screw and copy the set-up from that.

If it helps my metric Smart & Brown 1024 has a 4 mm pitch leadscrew, 12 divisions on the dial and uses gears of 12, 14, 15 and 18 teeth. My gears are in a nice bronze and appear to be straight cut at the helix angle of the screw.

It also has a spiffy little plate telling you which gear to use for which pitch and what number of divisions between engagements gives correct alignment of the cutting tool.

Having sorted out your dial system do make proper rack to store the gears on individual pins with clear labelling of the teeth counts. Its essentially impossible to see which gear is fitted so if you store them loose you will eventually end up trying to thread with the wrong gear fitted! If you have the same set as the Smart & Brown counting teeth to decide whether its the 14 tooth one on the indicator and 15 tooth one in the box gets old fast. I know a man who got it wrong.

Some lathes have a set up with all the gears permanently mounted on the shaft with a pull up and lock feature to select which one is in use. Theoretically better but there can be issues with making the reference line clearly visible at all positions of the dial.

I wonder how hard it would be to do an electronic one. Maths should be easy enough but an effective display clearly showing the approach to the engagement point might be hard. I'd probably go for a stepper motor driving a mechanical dial.

Clive

plumberpieco · Mar 26, 2020

This is from my Clausing Colchester manual of the same model.
Unfortunately there isn’t a good shot of the chart. Hope this helps.

matt_isserstedt · Mar 26, 2020

Hopefuldave said:
Metric requires several gears for the thread dial on a metric leadscrew, because metric works as length per thread (lead) not threads per length (TPI), and I've always found it easiest to leave the halfnuts engaged and reverse the lathe when swapping between inch/metric systems - most of the time for native threads too, unless it's a LONG thread.

Dave H. (the other one)

This is my tactic, forget about the threading dial, apply some waylube to the leadscrew, lock down the half nuts and traverse back and forth. Fast and you are guaranteed to never split the lead and it works for both inch and metric systems. No messing around with trying to recall the "rulebook" and you can get right to work.

janvanruth · Mar 26, 2020

Clive603 said:
If you can't find the factory data best alternative is to find a machine with the same pitch screw and copy the set-up from that.

If it helps my metric Smart & Brown 1024 has a 4 mm pitch leadscrew, 12 divisions on the dial and uses gears of 12, 14, 15 and 18 teeth. My gears are in a nice bronze and appear to be straight cut at the helix angle of the screw.

It also has a spiffy little plate telling you which gear to use for which pitch and what number of divisions between engagements gives correct alignment of the cutting tool.

View attachment 282814

Having sorted out your dial system do make proper rack to store the gears on individual pins with clear labelling of the teeth counts. Its essentially impossible to see which gear is fitted so if you store them loose you will eventually end up trying to thread with the wrong gear fitted! If you have the same set as the Smart & Brown counting teeth to decide whether its the 14 tooth one on the indicator and 15 tooth one in the box gets old fast. I know a man who got it wrong.

Some lathes have a set up with all the gears permanently mounted on the shaft with a pull up and lock feature to select which one is in use. Theoretically better but there can be issues with making the reference line clearly visible at all positions of the dial.

I wonder how hard it would be to do an electronic one. Maths should be easy enough but an effective display clearly showing the approach to the engagement point might be hard. I'd probably go for a stepper motor driving a mechanical dial.

Clive

stepper motor is only one step away from an electronic leadscrew..

Clive603 · Mar 26, 2020

janvanruth said:
stepper motor is only one step away from an electronic leadscrew..

Ha. Only if its a very, very long step!

Back around 1980 I built a scanner control system from standard Motorola CMOS ICs that included a unit which would effectively drive the threading dial. As I recall matters it had a phase lock loop, some grey code counters to do the clever bit, 3 D-Type flip flops and 6 small hexfets to drive the stepper and a cheap shaft encoder. Put the encoder on the leadscrew, add a 4 way switch to select the right count to mimic the gear in question and job done.

I imagine these days one of the cheap Arduino or similar boards would be the way to go.

In retrospect about 4 lumps of the whole system would have made a decent electronic leadscrew. All hardware and not too costly. If I'd twigged the potential I'd have taken greater care of my private copy of the circuit rather than leaving everything project related behind after a sideways "promotion".

Clive

Peter Colman · Mar 27, 2020

The Harrison M300 that I have has a dial that looks much the same as your photo, the box has a shaft inside it with a set of brass 'gears' that can be fitted to the shaft for different pitches, a chart on the box tells you which gear to use and where to engage the halfnuts.
If your leadscrew pitch is the same as mine, I can post details, if you don't get help from others, pm me and I will go measuring.

Clive603 · Mar 27, 2020

If its a 6 mm pitch screw the Colchester dial is quite likely to be the same as that fitted to Peters M300.

Attached is the relevant page from the later UK made Master 2500 which actually is a Harrison M300 with different badges.

8 divisions on the dial, gears are 14, 16, 18, 20 and 22, table shows the division numbers that can be used for re-engaging the half nut. All gears are permanently mounted. You slide the dial shaft up and down to engage them.

Colchester Triumph 2000 uses the same dial unit so if yours is a proper, all Colchester, Master and happens to have pitches not available on the rebadged Harrison that manual is for then you should be able to find a Triumph 2000 manual for details.

Clive

NewGunPlumber · Mar 31, 2020

SAG 180 said:
I've seen a metric leadscrew Master 2500 threading dial recently: they have multiple wheels at different ratios depending on the thread cut. It'll be while before I'm back in that workshop but I'll take some photos.

That would be great if you could get some photos!

NewGunPlumber · Mar 31, 2020

Clive603 said:
If its a 6 mm pitch screw the Colchester dial is quite likely to be the same as that fitted to Peters M300.

Attached is the relevant page from the later UK made Master 2500 which actually is a Harrison M300 with different badges.

View attachment 282998

8 divisions on the dial, gears are 14, 16, 18, 20 and 22, table shows the division numbers that can be used for re-engaging the half nut. All gears are permanently mounted. You slide the dial shaft up and down to engage them.

Colchester Triumph 2000 uses the same dial unit so if yours is a proper, all Colchester, Master and happens to have pitches not available on the rebadged Harrison that manual is for then you should be able to find a Triumph 2000 manual for details.

Clive

I found a manual and it looks to be a very similar setup and mentions the gears, the number of teeth and what numbers they can be engaged on. . . . . . Now to see if I can find some suitable gears and make the dial :-)

Yes yes the smart idea would be to leave the half nut engaged but I'm not that skilled or well endowed in the testicular department to cut an internal thread to a shoulder in a blind hole. I'm hoping to have the option of threading in reverse away from the shoulder by engaging in a cheater grove at the end of the blind hole.

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