Chester DB10 thread cutting ???

[Martin ConnellyParticipant @martinconnelly55370]

Howard, if the 127 gear is put in position a on the diagram then it becomes an 80/127 compound gear. Since 80 is exactly 2/3 of 120 it has a similar effect as a 120/127 compound.

Martin C

[Howard LewisParticipant @howardlewis46836]

As long as it allows Ian to cut Imperial pitches accurately, yes, do it!

Seems to be a fairly easy solution to the problem.

Possibly, others wishing to cut Imperial threads on a Metric lathe could obtain the gear and make any mods needed to fit it to their machine, even if means modding another 1 Mod gear to allow it to fit into the overall train on that particular machine.

Howard

[Ian Skeldon 2Participant @ianskeldon2]

Thank you Martin and Howard,

yes I think trying to get a selection of gears including the elusive 127 tooth gear would make life easier and more interesting. I would be up for boring out an existing gear and even bushing at a push. I have already looked at Arc but couldn't find anything.

At the moment there is no rush so I have the time to look around but one things is sure, I won't waste any more time (or spend any more money ) with Chester, they never did bother getting back to me, even to confirm that they couldn't help.

Thanks, Ian

[Ketan SwaliParticipant @ketanswali79440]

Ian,

Howard directed me to this thread. Also read Michael G's comment. I will look into the 127T gear and let you know as soon as I have clear information. I am currently out of office, and will be back on Monday.

Ketan at ARC.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Ketan Swali on 02/08/2018 17:35:20:

… I will look into the 127T gear and let you know as soon as I have clear information.

.

You, Sir, are a star

MichaelG.

[Ketan SwaliParticipant @ketanswali79440]

PM sent to Ian S for one piece which we have.

We have ordered some 127T gears for general selling, which will be with us by end of September. Price will be around £24.00 ~ £25.00 inc.VAT for this gear. It is heavy at around 710grams.

General dimensions are: Bore: 16mm, Keyway: 4mm, Width (thickness): 8mm, Width (thickness) near bore is: 10mm

Some pictures below:

Ketan at ARC.

[Michael GilliganParticipant @michaelgilligan61133]

That's excellent, Ketan

It compares quite favourably with this compound pair for a Boxford: **LINK**

https://www.ebay.co.uk/itm/Boxford-Lathe-127-100-Compound-Gear-Imperial-to-Metric/283071577644

MichaelG.

.

P.S. Unfortunately it's too big & heavy for my own current project

[Les Jones 1Participant @lesjones1]

Hi Michael,
You were correct when you commented the the figure I gave (In my post on 28/7/18 at 20:05) of 5/8" bore was odd on a metric lathe. I have just measured them again and they are 16mm so the 127T gear that Ketan has show will fit my DB-10G without any modofication. Could one of the modorators please edit my post on 28/7/18 at 20:05 and add the comment "(Correction the bore is not 5/8" it is 16mm )" after where I said the bore was 5/8".

Les.

[JasonBModerator @jasonb]

Done

[Les Jones 1Participant @lesjones1]

Thanks Jason,

Les.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Les Jones 1 on 03/08/2018 12:54:53:

Hi Michael,
You were correct when you commented the the figure I gave (In my post on 28/7/18 at 20:05) of 5/8" bore was odd on a metric lathe.

.

Thanks, Les … but ndiy actually deserves the credit for that comment.

MichaelG.

[Howard LewisParticipant @howardlewis46836]

Good work Ketan!

Thanks for all the details in the pics.

You may well make a lot of would be "Imperialists" happy

It shouldn't be too long before Ian can cut all sorts of Imperial thread pitches.

Just shows how members of this Forum get together to help each other.

Howard

[Les Jones 1Participant @lesjones1]

I will have to start going back to look at the posts rather than just relying on memory. That's twice in this topic I have credited the wrong person with a comment.

Les.

[Howard LewisParticipant @howardlewis46836]

Wonder if one of these 127T gears, bored / bushed down to 12mm, and with a 3mm keyway could be fitted onto a C2 or C3 mini lathe? (A 100T will fit onto the leadscrew, so wonder if there would be enough room? Must go and look, when the temperature drops a little)

If so, that would give a more exact change from Imperial to Metric, or vice versa, than the 63T gear, withh either Metric or Imperial leadscrew.

Howard

[Brian WoodParticipant @brianwood45127]

Howard,

I don't like bursting bubbles but the expected degree of improvement in thread pitch accuracy from the use of a 63 tooth wheel to one of 127 teeth in the gear train will be in the order of 0.003 mm per pitch turn, with all the other considerations in the thread cutting process being fully up to National Standards.

In old money that amounts to a trifle over 1/10 thou per pitch turn and I don't believe hobby lathes in this class have a lead screw capable of providing that level of precision in the first place. You would not be able to measure the improvement anyway with the sort of kit available outside a temperature controlled toolroom on the thread lengths that are likely to be involved

Regards

Brian

[Anonymous]

Posted by Brian Wood on 04/08/2018 15:20:16:

I don't like bursting bubbles but the expected degree of improvement in thread pitch accuracy from the use of a 63 tooth wheel to one of 127 teeth in the gear train will be in the order of 0.003 mm per pitch turn……..

Brian: I don't understand how you arrived at that number, could you explain the maths please? I would have thought the pitch error would be a percentage of the pitch, not an absolute number?

Andrew

[Brian WoodParticipant @brianwood45127]

Andrew,

Looking down the tables I worked out as direct results using 63 tooth wheels in the gear train for the Super C3 mini lathe with a 16 tpi leadscrew pitch [published in my recent book] this was the maximum order of error for pitches between 0.2 mm and 3 mm calculated and compared against the theoretical pitch that might be obtained with a 127 tooth wheel on the leadscrew. For the comparison, the error with a 127 wheel was taken as nil. Many were a lot less at < 0.001 mm which was as far as I considered it sensible to quote values.

The calculation was simply gearing ratio through the change wheels needed in each case, multiplied by the pitch of the leadscrew expressed in mm. Since there is no screwcutting gearbox on these lathes to include the complication of a further gearing ratio that was all that was necessary. Neil has used the same kind of calculation in his pdf for table in his book on the mini lathe; I extended his work a little to include DP and Module tables and ensured that wheel arrangements could be set up practically.

I hope that explains my thinking

Brian

[Anonymous]

Brian: Thanks for the explanation. Turns out we're calculating different things, which is why we get different answers. Just for a minute there I was worried my maths had gone askew.

I was looking purely at the error caused by substituting a 63 tooth for a 127 tooth, plus a 2:1 adjustment in the gear train. I wasn't considering other changes to the gear train to help compensate for the error in the 63 tooth gear.

Andrew

[Ian Skeldon 2Participant @ianskeldon2]

I am extremely impressed with the continued support from everyone. I will be following up Ketans mail and buying the 127 tooth gear on Monday.

I think the level of knowledge and depth of experience on this forum is amazing, even better is that people are willing to share their knowledge so freely.

I am indebted to so many people so please accept a BIG THANK YOU, to you all.

Ian

[Ian Skeldon 2Participant @ianskeldon2]

I apologise for taking so long to show the components I needed to cut 14 tpi for. Below is the collection of parts the small item was bought in, the other two made by myself. The solid bar still needs to be parted and faced then drilled and tapped to take the guage assembly but it is very nearly done now as you can see in the photo above.

My sincere gratitude to everyone that helped me to get this done.

Ian

Edited By Ian Skeldon 2 on 02/05/2019 18:39:17

Edited By Ian Skeldon 2 on 02/05/2019 18:39:46

[Anonymous]

Nice compact reg tester Ian

 

Edited By Mick Berrisford on 03/05/2019 09:04:40

[Brian WoodParticipant @brianwood45127]

Hello Ian,

That looks like a nice piece of work, thank you for showing us what the collective prodding of grey matter helped you produce as a result.

Regards

Brian

[Ian Skeldon 2Participant @ianskeldon2]

Posted by Mick Berrisford on 03/05/2019 09:04:08:

Nice compact reg tester Ian

Edited By Mick Berrisford on 03/05/2019 09:04:40

Thanks Mick. Hopefully it will get lots of use as I still have a few AA's with regs that do not perform well.

[Ian Skeldon 2Participant @ianskeldon2]

Posted by Brian Wood on 03/05/2019 10:01:31:

Hello Ian,

That looks like a nice piece of work, thank you for showing us what the collective prodding of grey matter helped you produce as a result.

Regards

Brian

Without the help from yourself and a few others I would have failed to get a satisfactory result. Of course I will still find a few more stumbling blocks with future projects I'm sure.

ATB

Ian

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