Hand taps for multi-start threads?

[hotponyshoes]

I've got some leadscrews/powerscrews that I could do with making up some running blocks for but I'm struggling to find a tap to suit if anyone knows a source?

It's an M20 thread but has 9 starts. 5mm Pitch, 45mm Lead.

Best I have found so far is a 3-start tap. I've not checked the thread geometry but, if it matches, could I just index that and run it through 3 times?

 

[Seadog]

The pitch increases as the number of starts increases. So no, you can't.

 

[hotponyshoes]

The pitch increases as the number of starts increases. So no, you can't.

Yea, I just looked at the 3-start tap again and it's 15mm lead. I need a 45mm lead

 

[Rrobson]

9 start?? That’s an unusual thread! It’s a wonder there’s space.

Doubtful you’ll get a tap off the shelf for that. You’ll either be making one yourself or going to a manufacturer with a blank cheque and your trousers round your ankles ready…

 

[Kram]

Sounds like an obscure spec perhaps they didnt want people reusing parts from it..
Whats the thread form, 30 degree trapezoidal?

Lathe job to make the nuts I think. With more starts, the cutting tool has a higher healix angle so needs more clearance which will mean a standard 5TR insert likely will not do it without modification.


Consider the moulded split delrin nut method.

Or cast brass nuts around a carbonised length of the bar. Heat to expand them off.

 

[Erie Fred]

Consider using the rod for fence post duty and buy new rod.....

 

[hotponyshoes]

9 start?? That’s an unusual thread! It’s a wonder there’s space.

Doubtful you’ll get a tap off the shelf for that. You’ll either be making one yourself or going to a manufacturer with a blank cheque and your trousers round your ankles ready…

20mm o/d rod so plenty of room (just) I think 10 would be tight

I might see if someone can make me a m20x45 tap and try indexing it 9 times..

Sounds like an obscure spec perhaps they didnt want people reusing parts from it..
Whats the thread form, 30 degree trapezoidal?

Lathe job to make the nuts I think. With more starts, the cutting tool has a higher healix angle so needs more clearance which will mean a standard 5TR insert likely will not do it without modification.


Consider the moulded split delrin nut method.

Or cast brass nuts around a carbonised length of the bar. Heat to expand them off.

I'm after nits for a high temperature application so not anything moulded.
Casting the nuts might well be a solution , would need to find a wide, shallow crucible to fit in my forge..

Consider using the rod for fence post duty and buy new rod.....

I can source/buy nuts for it easily enough but it would be nice to have a suitable tap 'in-house' for prototypes!

 

[Agroshield]

I might see if someone can make me a M20x45 tap and try indexing it 9 times..

A tap with 45mm lead would need to look more like a (spiral keyway) broach than a tap.

Do you need the nine starts? Grind off six of them from the screw to make the nut 'tapping' easier.

How high temperature? Would a cast (should that be 'cats' due to the 9 starts?) epoxy or phenolic nut work?