Chester DB10 thread cutting ???

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Chester DB10 thread cutting ???

This topic has 123 replies, 18 voices, and was last updated 3 May 2019 at 21:43 by Ian Skeldon 2.

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22 July 2018 at 21:36 #363411
Ian Skeldon 2
Participant
@ianskeldon2
Hi,

I have machined an internal bore to the correct diameter and depth, cut an overrun groove at the blind face, all without drama. Then I came to the task of cutting 14 tpi.

None of the diagrams make any sense to me, certainly not what I used many years ago, I will upload a (poor quality) photo showing the lathe instructions for screw cutting to see if anyone out there can enlighten me.

Thanks,

Ian

Edited By Ian Skeldon 2 on 22/07/2018 21:39:56
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22 July 2018 at 21:36 #9265
Ian Skeldon 2
Participant
@ianskeldon2
22 July 2018 at 22:09 #363417
Ian Skeldon 2
Participant
@ianskeldon2
A couple of slightly better photos;
22 July 2018 at 22:38 #363420
Anonymous
Hmmm, looks to me like the lathe is designed to cut a selected range of metric pitches. If you're prepared to accept a sloppy thread 14tpi is 1.814mm pitch, so you might just get away with 1.75mm over a short length. Otherwise I'm afraid you might be up the creek watching the paddle float away downstream!

On a more positive note there may be undocumented gear combinations that are closer, or other gears that may work better. But that is beyond my experience. I expect those with better knowledge of the intricacies of same will be along soon.

Andrew
22 July 2018 at 23:00 #363423
Neil Wyatt
Moderator
@neilwyatt
Top diagram gives feedrates for general turning nd facing under power feed (that's what the arrows indicate)

Bottom diagram is metric pitch along the bottom row.

A and B are the changewheels in the diagram, a selection of ratios at left in the top diagram.

Ratios are given in rows 2 and 3 of the bottom diagram, so its different to the top one – rather confusing!

Presumably 1,4,7 and 9 are some of the gearbox selector positions, with other positions giving further options.

Neil
23 July 2018 at 07:17 #363430
JasonB
Moderator
@jasonb
Without knowing the 7 gearbox ratios, spindle driver and lead screw pitch it would be hard for any of us to give a gear combination to get to your 14tpi. If you want closer than Andrew's 1.75mm pitch suggestion then you need to sit down and work out what is going on with the gears, levers and gearbox ratios and come up with something that gives a closer match.

Quick look and if you could get a 58T gear then put that in position B, 105T in position A and lever in No1 that would give you 1.810mm. A 3D printed one would go or buy a cheap one from one of the bearing suppliers.

IF you had a 55T in the gear set then 100/55 = 1.818mm which is quite close, lever pos 1 again. It is actually quite an easy layour to work out whats needed just convert the tpi to a mm pitch and see what fits in lever pos 1

I see that Chester only list it as giving metric pitches so you won't ghave got a 63T in the set of gears supplied.

This is the lathe for those not familiar with it.

Edited By JasonB on 23/07/2018 07:33:36
23 July 2018 at 07:50 #363432
Michael Gilligan
Participant
@michaelgilligan61133
Posted by JasonB on 23/07/2018 07:17:15:

This is the lathe for those not familiar with it.

.

Pardon my innocence, but, what is Chester's distinction between a closed gearbox and an open one … and which does Ian's lathe have ?

MichaelG.
23 July 2018 at 08:51 #363435
Martin Connelly
Participant
@martinconnelly55370
The two images on the linked web page have different gearboxes. I would suggest image 1 is a closed gearbox and image 2 is an open gearbox. Closed gearboxes can have oil in them for lubrication. Open need regular lubrication or drip oiling.

Martin C
23 July 2018 at 08:52 #363436
Les Jones 1
Participant
@lesjones1
With a ratio of 1:1 for A to B these are the feed values for the various gearbox settings. (Worked out from the posted list of settings.)

1 – 1.00mm
4 – 0.80mm
5 – 0.75mm (*)
7 – 0.667mm (2/3 mm to be exact.)
9 – 0.60mm (*)

(* These are calculated from the fine feed values but the ratio is slightly different for different table entries.)

Assuming that only gears A and B can be changed and that the gears shown in the table are the only ones available the best setting I can come up with is gear A 120 teeth, gear B 40 teeth and gearbox position 9. IF the feed for position 9 is exactly 0.6 mm then this will give a pitch of 1.80mm (14.11 TPI) Before cutting the thread I suggest measuring the feed by turning the chuck exactly 10 revolutions and measuring how far the carriage modes with the DRO or digital calipers.
Thanks to Neil for explaining what the vertical and horizontal arrows mean. (I was thinking it was another gearbox setting.) and to Michael for posting a picture of the lathe.

Les.

Edited By Les Jones 1 on 23/07/2018 09:39:55
23 July 2018 at 09:00 #363438
Bazyle
Participant
@bazyle
deleted- Martin already covered it.

Edited By Bazyle on 23/07/2018 09:02:00
23 July 2018 at 09:06 #363442
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Martin Connelly on 23/07/2018 08:51:42:

The two images on the linked web page have different gearboxes. I would suggest image 1 is a closed gearbox and image 2 is an open gearbox. Closed gearboxes can have oil in them for lubrication. Open need regular lubrication or drip oiling.

Martin C

.

Oh … is that all there is to it ?

Thanks

MichaelG.

.

I was guessing that there might be some functional difference; like the provision for swapping individual gears in the 'open' one. … Glad I asked!

Edited By Michael Gilligan on 23/07/2018 09:12:06
23 July 2018 at 09:27 #363446
larry phelan 1
Participant
@larryphelan1
I am surprised that your lathe will cut only Metric threads. I know that some machines are built this way,but for hobby use being able to cut the odd BSW thread is more than useful. My old Craftsman lathe cuts a fairly wide range of Metric and BSW threads and I find a need for both from time to time.

14 TPI is the old GB thread,and that comes along more often than you might think !

I managed to work out how to cut a few Metric threads which were not listed on my machine,by working out the ratios,using a calculator together with the gears supplied [too lazy to wake the old grey cells,what,s left of them ],so you might be able to do something similar. Even at this late stage BSW has not gone away !.
23 July 2018 at 09:30 #363447
larry phelan 1
Participant
@larryphelan1
Sorry,forgot to add that I do have a changewheel to go from Metric to Whit,came with the lathe.
23 July 2018 at 09:40 #363448
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Les Jones 1 on 23/07/2018 08:52:55:

… and to Michael for posting a picture of the lathe.

.

That's gracious of you, Les … but I was quoting from Jason.

MichaelG.
23 July 2018 at 10:35 #363452
Peter G. Shaw
Participant
@peterg-shaw75338
Excuse my ignorance, as I know nothing about lathe gearboxes.

Looking at the two images, they look to be two entirely different gearboxes. One looks like a nine position Norton style box with just the one lever, whilst the other appears to have two rotary levers, each with three positions.. Not only that, but the instructions on the casing appear different as well.

Does this mean that they provide different ratios? Or are they functionally the same, and providing the same ratios? I assume that the change from from normal turning to facing is done by a lever on the apron which also changes the ratio.

Peter G. Shaw
23 July 2018 at 13:15 #363469
JasonB
Moderator
@jasonb
I suspect you get the same number of pitches from either 1 lever x 9 positions = 9 ratios. 3×3 options on the knob version would also give 9 options.

Small lever to the left of the silver box on the apron selects turning or facing feeds, facing is usually haft the turning rate.
23 July 2018 at 17:00 #363488
Martin Connelly
Participant
@martinconnelly55370
With the information available the available ratios without using the 127 tooth gear is as below. Nearest to 14 TPI is 1.8mm pitch with a=120 b=40 lever in position 9. I would advise do not disengage the half nuts when cutting this thread. Is the 127 tooth gear a duplex and if so what is the tooth count on the other half or does it go in place of the 100 in position a? If you put a=127 b=70 and lever in position 1 you should get 14 tpi. Once again do not disengage the half nuts. Test the thread by scratching a bar before cutting.

Martin C
23 July 2018 at 17:43 #363493
JasonB
Moderator
@jasonb
Does it come with a 127T? did not see one mentioned
23 July 2018 at 18:16 #363497
Martin Connelly
Participant
@martinconnelly55370
I saw Larry mention he had a metric to Whit change wheel and thought it was the OP. If one is available the tables are as shown.

Martin C
23 July 2018 at 18:32 #363504
Brian Wood
Participant
@brianwood45127
Martin,

Do you also happen to know the leadscrew pitch as well?

Regards

Brian
23 July 2018 at 18:49 #363510
Martin Connelly
Participant
@martinconnelly55370
Sorry, no. This is all based on the pictures and information in this thread. That is why I suggested a scratch test, there could easily be errors.

Martin C
23 July 2018 at 19:02 #363514
Ian Skeldon 2
Participant
@ianskeldon2
Hi all and thank you so much for the help.

My lathe is the one with the single gear selector knob and nine holes selecting different ( spur ?) gears.

When I bought the lathe it was advertised as being able to cut both metric and imperial threads.

Sadly it looks as though Andrew and his description of my situation may be right. The thread needs to be 14tpi as the internal chamber will be subject to around 100bar air pressure and there is not enough material on the male component to turn it down and cut a metric thread on it, even if there was I would have to start this piece all over again with a smaller internal bore, oh bugger.

I called Chester to ask for advice, in short, I wasted the cost of the phone call, they didn't have a clue. So although my lathe cuts very true it will probably have to go at some point in the near future, to make way for something more capable.

Once again my sincere thanks to eveyone that tried to help me out with this.
23 July 2018 at 19:15 #363519
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Ian Skeldon 2 on 23/07/2018 19:02:04:

When I bought the lathe it was advertised as being able to cut both metric and imperial threads.

.

Did your keep a copy of that advert, Ian ?

… or was it just what they were displaying on the web ?

I have a nagging suspicion that the previous model was more versatile in the screw-cutting department.

Such is "progress"

MichaelG.

.

Edit: This took some finding, but it seems to confirm that the G version was capable of cutting Metric and Imperial threads: http://www.tphmachinetools.co.uk/products/548-new-chester-db10g/specs-pdf

Edited By Michael Gilligan on 23/07/2018 19:45:27
23 July 2018 at 19:34 #363525
Ian Skeldon 2
Participant
@ianskeldon2
Yep I can see a bit of a trend here, it was indeed as advertised on the website, sadly I never thought that saving the page might one day be useful.

Over the next few days I am going to cut a metric thread on a male bar and see how that fits into a female test piece, any slop at all means it's a none runner.
23 July 2018 at 19:42 #363526
Anonymous
PM sent – Andrew
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