Grinding a small Internal Trapezoidal threading tool

[Wongster]

Hello folks,

May I know if anyone here has ground a small internal trapezoidal threading tool for a nut?  I need to make a Tr8x2 brass nut for an SLA 3D Printer I backed and received.  The nut that came with the printer is rather sloppy and those I bought from China are the same... Buying brand name nut is too costly for the cheapo printer.  So I am considering grinding my own tool, and at the same time, learn from doing it.

The tap drill should be 6.5mm.  Pitch of the lead screw is 2mm single start.  From the diagram I found online:

   

P = 2mm
H1 = 0.5P = 1mm
and the flat top = 0.366P = 0.732mm
Thread angle = 30 degree
(hope I get these correct)

I was trying to find pics online to sort of give me an idea how such a tool would look like before attempting to grind one myself.  I'm still a new hand in grinding HSS tool.  The last tool I ground was at least 4-5 years ago.  

Also, what size blank should I start with?

Best regards,
Wong

[TomG]

For a thread that small, you might be better off making a tap. It's a lot easier to grind a tool to cut an external thread than an internal, especially one that small. Another option would be to swage the existing nut to a screw to take out the play and then lap it to whatever clearance you desire.

Tom

[Wongster]

Thanks Tom.

May I know how I can "swage the existing nut....."?

I did order a tap for the nut which I think will only reach me a week or 2 after chinese new year. Buying from china is a hit and miss affair, so I'm not counting on it to achieve a better fit. If it does, I'll be happy. If it isn't, no big deal; its only a few dollars.

I watched some videos on making such taps using identical leadscrew as the tap. I don't have those grinding and cutting wheels. Maybe I can use my bench grinder for that after milling the slot on the mill.

Regards,
Wong

[TomG]

It depends on the shape of the nut. I've squeezed things like that with a three jaw, or if that won't do it you may have to make a die that you can use in your mill vise. Anything that compresses the nut evenly will do.

For a tap, I would make it out of O1 so you can do all the machining. O1 should be hard enough to cut brass as is, or you can harden it with an oil quench.

Tom

[randyc]

How about slitting one side of the nut first and then squeezing ?

[4gsr]

I know this is a old thread, not that old.

Here's a list of taps available on eBay you could use the cut this thread.

https://www.ebay.com/sch/i.html?_from=R4...p&_sacat=0

Ken

[Wongster]

Thank you guys. The tap arrived from china. I’ll find time to make the brass nut, failing which I would just use the printed one give to me by a friend. He gets good result from using the PLA nut.

[Vinny]

PLA doesn't retain its shape or composure when it gets warm. PLA prints left in a car on a sunny day tend to melt or stretch outta shape, so it doesn't take much.