# 33 x 3.5 mm threads



## woodfarmer (12 Oct 2013)

Hi

I am hoping to take up wood turning at long last and I would like to make a few accessories for it. In particular a couple of faceplates as I like working with them. Sadly my old Holbrook will only do inch pitch threads and the nearest I can get to 3.5m between threads is 3.648571429mm (7 pitches to the inch). I could make the threads sloppy but does anyone know how I could get around this? I looked online and taps are about £120 a piece, so could be cheaper to buy the faceplates ready made.


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## CHJ (12 Oct 2013)

I have the same frustration with my little lathe, I need another 80 tooth gear to get to my 6TPI and I'd need to crank manually due to high gearing on the lead screw box.

Solution for me has been to buy ISO backplates and use these to to provide the thread.

You might find it economical to just buy the thread adaptors/inserts for one of the popular chucks and use these to turn a threaded sleeve for your projects.


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## woodfarmer (12 Oct 2013)

CHJ":2t1t8mrd said:


> I have the same frustration with my little lathe, I need another 80 tooth gear to get to my 6TPI and I'd need to crank manually due to high gearing on the lead screw box.
> 
> Solution for me has been to buy ISO backplates and use these to to provide the thread.
> 
> You might find it economical to just buy the thread adaptors/inserts for one of the popular chucks and use these to turn a threaded sleeve for your projects.



I can do the 6 TPI you need easily. from the gearbox I can select from 4 to 28 TPI.

Problem with the 33mm is that it is bigger than the others, so an adapter would stick out. My preference is for bigger bowls so a bit of a worry about stressing the head bearings. Maybe somewhere it might be possible to put a 127 tooth gearwheel or something similar.


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## Robbo3 (12 Oct 2013)

M33 x 3.5 (plug/bottom?) tap - £21.18
- http://www.rdgtools.co.uk/acatalog/WOOD ... _TAPS.html

P & P to the continent £9.50. Free to mainland UK.

Edit:

Beall M33 x 3.5 taper tap - £16.07 + VAT + P & P 
- http://www.toolpost.co.uk/pages/Chucks_ ... SpindleTap

HTH


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## CHJ (12 Oct 2013)

woodfarmer":2i76ntkn said:


> .....Problem with the 33mm is that it is bigger than the others, so an adapter would stick out. My preference is for bigger bowls so a bit of a worry about stressing the head bearings. Maybe somewhere it might be possible to put a 127 tooth gearwheel or something similar.



I swap between 120 and 127 for the imp./metric change.

I was thinking of just turning down an ISO backplate to take your other faceplates etc.
Even if you mounted a faceplate on the front of an ISO backplate you would not be overhanging your spindle nose as much as a standard chuck would.





ISO chuck backplates.


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## woodfarmer (12 Oct 2013)

Robbo3":3cus5ro2 said:


> M33 x 3.5 (plug/bottom?) tap - £21.18
> - http://www.rdgtools.co.uk/acatalog/WOOD ... _TAPS.html
> 
> P & P to the continent £9.50. Free to mainland UK.
> ...



Thanks, but these taps are for cutting wood to mount onto a the headstock spindle. What I want to do is tap a thread in steel to mount a faceplate on the spindle.


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## woodfarmer (12 Oct 2013)

CHJ":38jd3g3e said:


> woodfarmer":38jd3g3e said:
> 
> 
> > .....Problem with the 33mm is that it is bigger than the others, so an adapter would stick out. My preference is for bigger bowls so a bit of a worry about stressing the head bearings. Maybe somewhere it might be possible to put a 127 tooth gearwheel or something similar.
> ...



Many thanks, this may well be the way for me to go.


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## Tinbasher (28 Mar 2014)

woodfarmer":ayfkcjfy said:


> Robbo3":ayfkcjfy said:
> 
> 
> > M33 x 3.5 (plug/bottom?) tap - £21.18
> ...



Although they say you can use these to tap into wood. They don't say they are anything different to a "proper" tap. Personally I would give it a go, the hardest thing with a large tap is ensuring that you start it concentrically so the faceplate doesn't have a wobble.


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## chipmunk (31 Mar 2014)

Axminster do a 75mm M33x3.5 faceplate for £13.44 which may be slightly cheaper...

http://www.axminster.co.uk/axminster-faceplate-75mm

The other way is to try other change-wheel combinations on your lathe. My old Myford is completely imperial but after buying a couple of new 21-tooth gears I am now able to cut metric threads, including 3.5mm pitch, with a tolerance which is close enough i.e. 0.05%.

HTH
Jon


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## woodfarmer (31 Mar 2014)

chipmunk":3itz4l5r said:


> Axminster do a 75mm M33x3.5 faceplate for £13.44 which may be slightly cheaper...
> 
> http://www.axminster.co.uk/axminster-faceplate-75mm
> 
> ...



Thanks. I have already bought some of the axi faceplates. may well be the easiest way for me to go, doubt I will need many.

Change wheels for my 90 year old Holbrook are unobtanium, may end up making some.


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## chipmunk (1 Apr 2014)

woodfarmer":1n06tzqi said:


> Change wheels for my 90 year old Holbrook are unobtanium, may end up making some.



Ok, I know you can do 7 TPI but have you tried all the options of what you can do with other combinations of your existing gears? 

Although the 21-tooth gears get me within a "gnats piccolo" I was able to get pretty close to 3.5mm without.

Just to give you an idea, my ideal set up for 3.5mm is...

60, 20-35, 40-21, 50 which gives me 3.5004375 mm (0.0125%)

but...

55, 25-20, 60, 40 will give me 3.4925 (-0.21229%)

..I'm pretty sure this would probably be close enough for a few threads on a face-plate. 

The Axminster chuck guide says that the T38 thread has 24mm of thread or 6.8 pitches. So let's say 7 pitch periods with 0.25% error would lead to 1.75% accumulated error over the length of the threaded portion or 0.06mm (i.e. 2.4 thou). If your lathe was used when Pontius was a Pilot then your leadscrew could easily have this error through wear I reckon anyway :wink: 

...and this was found with a couple of minutes "trial and error" with Excel.

Give it a go
HTH
Jon


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