Cormak TU2807v gearing issues

[paul_goParticipant @paul_go]

Hiya everyone

Very new member here and apologies for the novel I’m about to post here.

I have a Cormak TU2807v. Which I believe is identical to the Optiturn TU2897v lathe. It has a 40T spindle hear and has a 3mm lead screw.
I’m trying to set up the change gears to cut 16 TPI. According to the gear chart on the lathe, the arrangement should be:

H – 30

60 – 70

65 – H

Unfortunately, this arrangement appears to be impossible to assemble on my machine.

The issue is that the 30-tooth gear will not reach the fixed 40-tooth spindle gear. Even with the other gears correctly meshed, there is still approximately a 7 mm gap between the 30-tooth gear and the spindle gear. In addition, the mounting stud for the 30-tooth gear contacts the belt drive pulley housing before the gears can be moved any closer.

As a result, I cannot use any gear arrangement that requires the 30-tooth gear to mesh directly with the spindle gear.

From the gearing plate on the lathe that means every metric thread cannot be cut

Can anyone out there with experience on these machines help me move forward with this ?
I have attached photographs to illustrate the clearance issue and the interference with the pulley housing.

I would greatly appreciate any advice or technical information anyone can provide.

Thanks

Paul

[JasonBModerator @jasonb]

The 30T is just an idler you can put something larger in it’s place provided you have the length in the banjo slot, try a 40T

Another option which would sort teh stud hitting prblem and maybe allow the banjo to go back further would be to put the 60-70 pair on th efirst stud, the 30T on the second stud and mesh the 30T with the 65 on the leadscrew

60-70

30-H

65-H

[paul_goParticipant @paul_go]

Hiya Jason

Thank you for the reply. No the 30T is supposed to mesh with the other gears in the arrangement to drive to lead screw. The idler is to the left marked as H on the gearing plate

if I put in a larger gear like the 40T the gearing ratio won’t be the same and won’t thread 16tpi

 

[paul_goParticipant @paul_go]

I’ll try the other arrangement you suggested

thank you👍

[JasonBModerator @jasonb]

No the H just represents spacers.

An idler gear is one that is on it’s own and just fits between two others, it is the relationship of those two other gears that determines the gear ratio.

[JasonBModerator @jasonb]

This is the maths. gears that matter underlined in orange. The 30T does not come into th emaths so can be changed for anything that fits

[paul_goParticipant @paul_go]

Awesome

thank you. I’ll try this out 👍

 

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