Chester DB10 thread cutting ???

[Ian Skeldon 2Participant @ianskeldon2]

Aagghhhh I think something is wrong here, I have a tumbler driving a 70T, driving a 80T with a 120T on the same shaft (a) driving the 40T on the feed screw gear box (b), I have selected position 9 on the gear box and a scratch test shows about 24/25 tpi.

Is there something obvious I am missing or is it possible that the label stuck on the machine is the wrong one. Right now any ideas are very welcome.

Please see diagram below showing the number of teeth on that given position.,

Thanks, Ian

[Martin ConnellyParticipant @martinconnelly55370]

120 tooth gear should be larger than 40 tooth gear. Have you got them the wrong way round because that's what the illustration looks like?

Martin C

[Les Jones 1Participant @lesjones1]

Can you can confirm that the 80 tooth and the 120 (Which are on the same shaft.) rotatate exactly one revolution for two revolutions of the chuck ? Can you confirm that the 40 tooth rotates three revolutions for two revolutions of the chuck ? Can you confirm that with the gearbox in position one that the leadscrew rotated exactly one revolution for one revolution of the 40 tooth on the gearbox input ? Can you confirm that with the gearbox in position nine that the leadscrew rotated exactly three revolutions for five revolution of the 40 tooth on the gearbox input ?

(I am assuming that the picture does NOT show it set up with the actual gears. I assume you have just used a picture with some other setup and marked it wit the gears that you have installed.)

Les.

[Les Jones 1Participant @lesjones1]

Hi Martin,
I was also thinking that Ian could have the 40 and 120 tooth gears swapped over but when I worked it out I would expect that to give 127 TPI. (14.11 x 9) Also the ratio of the TPI values between gearbox position 1 (1 : 1) and gearbox position 9 (1 : 0.6) Ian quoted about 22 TPI in gearbox position 1 and about 24 or 25 TPI in gearbox position 9.
If he had 22 TPI in position 1 then I would expext about 37 TPI (22/0.6 = 36.66)
Looking more closely at the chart in Ian's second post (22:09 on 22/07/18) there seems to be a difference between the ratios between fine feed and screwcutting. There may be a control that changes the ratio or fine feed may drive the carriage via the rack and pinion rather than the leadscrew.

Les.

[Howard LewisParticipant @howardlewis46836]

Could you mesh a 1 Mod 127T gear earlier in the train (where it wouldn't hang outside) and fix it one of the others, to compound it?

My larger Far Eastern lathe uses a 120/127T compound gear as an idler to cut Imperial pitches from a Metric Leadscrew.

Alternatively, if you were prepared to make/buy two 0.75 or 0.5 Mod gears, the 127T would be smaller, and would mesh with each other, but the smaller would need to fixed to one of the other gears in the train as a compound gear.

The smaller would probably need to be compounded with one of the smaller 1 Mod gears in the train. If you could a fit in a compound gear, with the same number of teeth as one already in the train, but 1 Mod on one and 0.75 Mod on the other, (to drive the 127T).You might need a spacer behind the 127T to bring it line with its partner.

Once available, you could then cut threads with Imperial pitches that are accurate as that of your Metric Leadscrew.

You will still nee to do the maths / experiment to arrive at the required pitch.

Hopefully the gears have keyways, rather than the pin arrangement used on Myford ML Series.

As an aside, after making two 100T gears for my mini lathe, I had to modify the cover (cut and extend) to safeguard one of them, as part of the minor modifications needed.

Just a thought or two.

Howard

[JasonBModerator @jasonb]

I think Ian has just been using one photo and adding the numbers, look at the first photo on this page and it's the same as the ones with the writing on them.

[Howard LewisParticipant @howardlewis46836]

So replace the 80/120 compound Idler with a 120/127 one, like on my BL12-24, if the slots will allow correct meshing?

Howard

[Ian Skeldon 2Participant @ianskeldon2]

Hi,

Yes the photo is the original photo, but I have edited it to show the current arrangement.

Howard, sadly I can't replace anything with a 127 tooth gear as I don't have one, the gears that I do have are listed much earlier on in the thread.

I will try to get another photo showing the arrangement but be aware that the 120 tooth gear will mask the 80 tooth gear.

Thanks again to everyone trying to help me with this issue.

Ian

[Ian Skeldon 2Participant @ianskeldon2]

Les, one full revolution of the chuck turns the 120 tooth gear 1/2 a revolution, so yes two full revolutions of the chuck, will rotate the 120 gear a full revolution. More information to come shortly.

Edited By Ian Skeldon 2 on 30/07/2018 18:47:43

[Ian Skeldon 2Participant @ianskeldon2]

Hi Martin, the photo is showing the old gearing but the writing is correct, Les your maths is spot on, the 40 tooth is doing 3 revolutions to every 2 revolutions of the chuck.

[JasonBModerator @jasonb]

Ian, are you engaging the half nuts for screw cutting or are you using the feed lever?

Feed lever takes the leadscrew drive through  a reduction gear to the rack on the front of th ebed. Half nuts drive the carrage direct from the leadscrew.

 

Edited By JasonB on 30/07/2018 19:23:18

[Ian Skeldon 2Participant @ianskeldon2]

Les with the gear box in position 1, 1 revolution of 40 tooth produces one full revolution of the leadscrew, however 5 full turns of the 40 tooth gear produces aprox 2 1/2 (2.5) revolutions of the leadscrew.

I have taken another pass and the pitch is now easier to measure and comes out at 0.8mm giving if I am right about 32 tpi?

[JasonBModerator @jasonb]

Are you sure it's not 0.72mm pitch which would be what I would expect if the feed lever were being used rather than the half nuts being engaged with the big black lever.

Edited By JasonB on 30/07/2018 19:44:09

[Martin ConnellyParticipant @martinconnelly55370]

Ian, you should have a lever on the carriage that protrudes toward you. This selects automatic feed in one position, possibly has a central neutral position and has a position for threading. You will not be able to use the half nut lever if the feed/threading selector is in the feed position. Near this is another lever that engages and disengages the half nuts to move the carriage for threading. If you do not have the leadscrew turning then moving the carriage with the handwheel may be needed to engage the half nuts. If the half nuts are engaged and the leadscrew is not turning it will seem that the carriage is locked in position. Have a play around with these carriage levers to make sure you fully understand their purposes. Do this with power off and turning the chuck by hand to avoid running the carriage into the head until you are happy with what is going on.

Martin C

[Ian Skeldon 2Participant @ianskeldon2]

Jason your right, I have been using the feed lever. I used the halfnut engage lever the first time and the meshing was so bad I assumed I had got it wrong Doh…

Using the half nut lever does indeed produce what looks like 14 tpi, give or take. However the lathe slows down and even stalls occasionally, even with a pretty light cut. I have been using the slowest speed available and would like to keep the half nuts engaged as they really do seem very agricultural when engaging at the start of each cut.

So this problem was caused by the most commonly known fault, the user, my sincere apologies to everyone who has tried to work out what was going on. Also I am most grateful to everyone that offered help and advice throughout the whole of the thread (pun intended).

Ian

[Les Jones 1Participant @lesjones1]

Hi Ian,
The half nut will only engage with the leadscrew when it's thread is lined up with the thread on the leadscrew. You need to gently move the half nut lever and wait until it falls into the thread. I would normally turn the lathe by hand when cutting a thread up to a shoulder. (Or use the method of running the lathe in reverse starting on the relief at the shoulder. To do this you need the tool cutting the back of the thread or at the front with the tool upside down. Someone posted a link to a youtube video showing this method recently in another thread.)

Les.

Edited By Les Jones 1 on 30/07/2018 20:48:22

[Martin ConnellyParticipant @martinconnelly55370]

Ian, rule one for cutting imperial threads on a metric leadscrew is do not disengage the half nuts until the thread cutting is complete. If you do not have a reverse option on the motor you need to wind everything back by hand for each pass.

The next rule for thread cutting is if you have a choice of feed setups from the motor use the slowest to give the highest torque. Threading will be moving the carriage up to 20 times faster per revolution of the spindle compared to auto feed. It requires plenty of torque in the drive train. Slowing the motor electronically reduces available torque so should be avoided when cutting a coarse thread.

Stalling the lathe may be due to the carriage gibs being too tight or that a carriage lock is not fully released. A good quality way oil on the lathe bed is also a good idea.

Martin C

[Les Jones 1Participant @lesjones1]

Martin beat me to pointing out about not disengaging the half nut. One more point is retract the tool before reversing the lathe as the backlash in the gearing will mean that the tool will be in a different position with respect to the cut thread in the reverse direction. Also take it far enough from the start of the thread in reverse so that all the backlash is taken up in the forward direction before the tool starts to cut on the next pass.

Les.

Edited By Les Jones 1 on 30/07/2018 21:31:41

[Ian Skeldon 2Participant @ianskeldon2]

I am so impressed at the fantastic help I have received. I have just made a few more cuts leaving the halfnuts engaged, I tested first how quickly the carriage stops when the stop button is pressed and it's almost instant.

Result, now cutting a decent thread with the half nut constantly engaged.

Thank you so much to so many for sorting this out for me, I am very grateful.

Ian

[Mick B1Participant @mickb1]

Just seen the tail-end of this thread. If you're screwcutting with the halfnuts permanently engaged, you can gain consistency by stopping a turn or two short of where you want thread runout, and finish rotating by hand to get to the same point each cut. If you've a bit of round bar that fits the square chuck socket, that can help as a handle.

[Martin ConnellyParticipant @martinconnelly55370]

Glad it's sorted. When the job is done why not get some card and draw a 127 gear outside diameter on it and offer it up to see if it can fit in position a. If it does it would be worth getting one for future requirements. It would allow exact tpi setting. The spreadsheet to work out tpi or metric pitch thread settings is easy to write or if you're not confident writing one I can email one to you. Send a message with your email and details of the spreadsheet program you have if you want it.

Martin C

[Martin ConnellyParticipant @martinconnelly55370]

I've smartened up the spreadsheet of thread settings for the DB10 and created a jpg file but am limited to the quality of jpg that I can create from the spreadsheet. This is the result, clearer copies are available but would have to be emailed as something other than a jpg.

Martin C

[Howard LewisParticipant @howardlewis46836]

Ian,

In the Arc Euro catalogue, there is mention of a 127T gear in the description of the SC4, for cutting Imperial threads..

Don't know if one would be obtainable as a spare. They do list some spares for the SC4 on their website.

If ordered specially, it might take six weeks or so to obtain from China

"Little Machine Shop" mention one as part of the complete set of change gears for the SC4, that they sell; ($169) but they are in USA..

The gears are stated to be 1 Mod, so will be 129mm diameter, and likely to have a 4mm keyway.

(If your gears are 1 Mod and have a 3mm keyway, the easy way is to cut another 3mm keyway, opposite the existing 4mm one).

If you could get one and mate this with the 120T, using the combination as an idler would allow you cut a larger range of Imperial threads with accurate pitch.

Howard.

 

Edited By Howard Lewis on 01/08/2018 10:10:38

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Howard Lewis on 01/08/2018 10:09:57:

Ian,

In the Arc Euro catalogue, there is mention of a 127T gear in the description of the SC4, for cutting Imperial threads..

Don't know if one would be obtainable as a spare. They do list some spares for the SC4 on their website.

.

If Ketan could be persuaded to keep this as a stock item … purist screw-cutters would happy

MichaelG.

.

https://www.arceurotrade.co.uk/machineparts/Super-C4-Parts-Diagram-and-List-2014.pdf

Edited By Michael Gilligan on 01/08/2018 10:29:59

[Howard LewisParticipant @howardlewis46836]

Michael, Ian.

Had looked the range of SC4 spares carried by Ketan, but no mention of gears. The manual showed

Item 73 "Transition Gear" 2 off, without any detail of tooth count.

Being 1 Mod, the SC4 gear should mesh satisfactorily with Ian's existing change gears.

It would be good if they are 16mm bore (Cannot believe that those for the DB10 are 5/8" )  (Correction the bore is not 5/8" it is 16mm) If the 127T SC4 gear is not, it ought to be possible to bore / bush it to match the other gears on the DB10. Similarly, if the DB10 has other than a 4mm keyway, it should be fairly easy to add a suitable one, to allow it to be compounded with the existing 120T.

With a 120/127 compound as an idler (As my lathe has) a wide range of Imperial threads could be cut, (After some maths, or experimentation, no doubt)

If you are prepared to go down that route, there is light at the end of the tunnel! (But, typically, someone with a torch bring more work!)

Howard

Edited to get rid of that confounded emoji!  MUST remember to leave a space before the final bracket

Edited By Howard Lewis on 01/08/2018 11:26:07

Edited By JasonB on 03/08/2018 13:23:18

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