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BSW 1 1/2 x 6

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John Cheney14/02/2021 11:37:08
3 forum posts

The lathe I'm using is a Toss 26A. Removed from production (I'm guessing) when the bed slide tightened for accuracy nearer the chuck caused the rest of the movement to be tight. So, not super accurate!

However, I've used it to great effect in making parts I could not otherwise buy.

I would like to use it to make metal parts for my wood lathe. I could not get a chuck with a BSW 1.5 x 6TPI thread to fit the head stock, so I bought one with a M33 thread with the intension of boring it out and re- threading it BSW.

I have a bar (S1 2M- SCLCR09).

looking at the bar I don't think it is big enough to hold an insert deep enough to cut the required thread depth. Would I be better to just get a rombic 55 degree tip rather than a toothed insert?

I really don't want to spend mega bucks getting this tooling as I may only need to do this once or twice.

Any help would be greatly appreciated.

larry phelan 114/02/2021 18:32:54
1170 forum posts
15 photos

Could you not just make a simple boring bar and use a HSS tool bit ground to 55* ?

I made two backplates for my lathe like that ,simple and cheap.

Martin Connelly14/02/2021 18:55:43
2123 forum posts
222 photos


This is what I did to a broken BSW tap to use it for my backplate threads. I wanted 8 TPI BSW x 1.75", this started off as 1" x 8 BSW tap. If you could get a scrap 6 TPI tap with just one good tooth it would make a useable tool.

Martin C

David George 115/02/2021 08:02:42
1808 forum posts
503 photos

You can get a tap from Tracy Tools for about £35.00 plus delivery.


Tony Pratt 115/02/2021 08:32:15
1929 forum posts
12 photos

If you go down the tapping route you will need to screw cut it first so why not just make a single point internal screw cutting tool. I'm pretty sure you will not get a screwcutting tip for your S1 2M- SCLCR09 boring bar


Chris Gunn15/02/2021 09:14:58
429 forum posts
27 photos

John, I have a set of 1/1/2" x 6TPI taps you could borrow, but you will need a big tap wrench!!

Chris Gunn

Ian Parkin15/02/2021 10:07:51
1016 forum posts
236 photos

It’s nigh on impossible to cut this size thread in steel with a tap without first screw cutting a close impression of the thread.

i cut lengths of alloy studding this size and run a die down to clean it up after screw cutting and do it in the lathe and the motor (3hp) at 50 rpm is close to stalling and using all my strength to hold on the die holder

JohnF15/02/2021 10:38:23
1146 forum posts
189 photos

I would forget taps and go down Larry's route making a boring bar with a HSS tool ground to the thread form and dependant on the capabilities of your machine I would consider setting the top slide to 27 1/2 deg thus reducing cutting forces on a large thread.

The first thing i would make is a gauge to ensure your new back plate will fit your wood lathe spindle, To do this measure the spindle using the 3 wire system then make a male duplicate to the same dimension over the wires the as long as that fits your female backplate thread you know it will fit the spindle.


old mart15/02/2021 17:28:30
3720 forum posts
233 photos

As already mentioned, a tap would be quite usable, but at that size, would be very difficult to turn. I bought a much smaller 3/4 x 5 ACME tap from Tracy Tools, it had a very long taper, and I tried it out in an aluminium test piece. I found it so hard to turn that I single pointed the actual nuts using an 8tpi ACME running at the 5 tpi and took out as much metal as possible from the gunmetal. The threads were about 3/4 finished before tapping which was still hard, but doable.

I think I would prefer to tap cast iron than steel using this method.

John Cheney21/02/2021 11:30:49
3 forum posts

Hi Everyone,

Thank you all again for taking the time to reply.

Now waiting on a time slot to go and "play" in the workshop!

I'll let you know how I get on



Chris Gunn21/02/2021 20:34:10
429 forum posts
27 photos

John, Good luck with it, just to clarify my earlier post, on the assumption you would still screw cut the thread first, you could then bring it to size using a tap, which I can lend you.

Chris Gunn

D.A.Godley21/02/2021 22:33:04
120 forum posts
39 photos


Would you please pm me regarding the following,




John Cheney23/02/2021 12:37:41
3 forum posts

Hello again!

Just to let you know that I'm not a thread virgin anymore!

I ground a TC tip to match the set screw thread and then cut the chuck thread.

I was mistaken when I said I had a taper tap, it is actually a 2nd cut.

When I checked the turned thread with the tap, only a tiny amount of material was removed and with ease..... to say I'm pleased is an understatement!

Thanks again for your help.


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