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1 TPI thread on a Colchester Bantam

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vintagengineer18/01/2018 22:12:13
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419 forum posts
6 photos

I need to make two brass nuts and two short shafts to suit with a 1 TPI multi start thread.

Any suggestions for the gear train set up?

Thanks.

Hopper18/01/2018 23:22:42
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2477 forum posts
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Leadscrew TPI?

Standard headstock spindle gear size?

Edited By Hopper on 18/01/2018 23:24:19

Chris Evans 619/01/2018 07:25:23
1161 forum posts

Have you got a hand crank? That would be going along a bit quick under power.

JasonB19/01/2018 07:35:09
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Whatever gear train you go for make one gears teeth divisible by the number of starts then you can use that to index each start. Crank the leadscrew not the spindle and make sure you have clearance under the tool to clear the steep helix angle

Hopper19/01/2018 08:43:15
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2477 forum posts
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QC gearbox or do you have a full set of change gears?

Martin Johnson 119/01/2018 08:49:01
54 forum posts
1 photos

I am in the (very extended) course of doing a similar thing. My thread started as 0.75" pitch, 4 start 1" OD but has become 0.6" pitch, 3 start, 1" OD - it is for a steering box and I decided for other reasons to give the box more ratio. I decided to go down the thread milling route and have done the job on my TS mill. I am using a modified gear cutter (No. 1 which is near to rack form) to cut an ACME form thread. The nut (which I think is the more difficult job) is to be cast in whitemetal inside a bronze housing. There are some pictures on Flickr starting here:

https://www.flickr.com/photos/140734312@N06/37334008234/in/album-72157669955074511/

Hope that helps.

Martin

Martin Johnson 119/01/2018 08:52:01
54 forum posts
1 photos

Just realised that the link in my last post only takes you to the one photo. Scroll down the page and go the album, and the screw milling is toward the end of the album.

Martin

Clive Brown 119/01/2018 09:47:07
121 forum posts
5 photos

Prof. Chaddock gave a detailed description of producing a large pitch thread in a lathe for his Quorn construction series in ME and book.

IIRC, he chose milling with a toolpost mounted spindle. The leadscrew was driven by adapting the lathe drive, using a large, home-made plywood pulley to get an overall very low ratio. I think that he discounted "handraulic " drive because of the time traverses would take on the fairly long thread.

I think machining an internal thread would be tricky. The Quorn uses a peg to engage the thread.

vintagengineer19/01/2018 13:07:44
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419 forum posts
6 photos

Nice work. How did you cast the white metal thread? That would be easier for me as one set is 18mm dia and the other is 12mm!

Posted by Martin Johnson 1 on 19/01/2018 08:49:01:

I am in the (very extended) course of doing a similar thing. My thread started as 0.75" pitch, 4 start 1" OD but has become 0.6" pitch, 3 start, 1" OD - it is for a steering box and I decided for other reasons to give the box more ratio. I decided to go down the thread milling route and have done the job on my TS mill. I am using a modified gear cutter (No. 1 which is near to rack form) to cut an ACME form thread. The nut (which I think is the more difficult job) is to be cast in whitemetal inside a bronze housing. There are some pictures on Flickr starting here:

https://www.flickr.com/photos/140734312@N06/37334008234/in/album-72157669955074511/

Hope that helps.

Martin

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