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plunger
10-04-2010, 01:27 AM
I want to try and make a new brass nut for my 13x40 chineese lathe.
What confuses me is that it seems to be a strange size.If I mike the leadscrew it is 14.35mm It seems to be a 10tpi.I cant find any info on any thread this size.
Would this be a stub acme or a trapoizial thread or is that just a metric name for a acme thread.I will be trying to turn this in my lathe as I cant buy a tap or threaded rod here in s africa. We arent spoilt for choice like you guys.
Would this work?
Mike the size of hole in existing nut and bore same size hole in new brass nut.
Make a boring tool out of 12mm silver steel and machine front down to 8mm and cross drill to accomadate a 4mm round hss bit . Use the existing leadscrew as template for grinding the 4mm hss. Then if I tilted by eye (thumbsuck style) the 4mm hss to try to cater for the helix. Then if I just went for it untill the nut started screwing on.
Would this work or is this a very flawed way of doing things? This is for the tailstock
Regards Eugene

The Artful Bodger
10-04-2010, 02:04 AM
Eugene, does it have to be brass or could you use the method recently described here telling how to effortlessly mould a nut from Acetal?

winchman
10-04-2010, 02:06 AM
It might be easier to replace both the nut and the leadscrew with something of a regular size. The function of the tailstock won't be affected except for the slight change in the travel per revolution of the handle. How hard would that be?

Black_Moons
10-04-2010, 04:01 AM
Grind the helix clearances into the bit, Don't try and tilt the boring bar, that won't work very well. You could rotate a round bit in a boring bar, But generaly you just grind the side clearance excessive to clear the helix.

plunger
10-04-2010, 07:35 AM
I was very curious to know if I could do this in acetal and asked if vesconite (a s african invention could be used for this as its self lubricating and doesnt absorb water but apparently its melting point is to high What do you think? Would it stand up to say drilling a 30mm hole in steel. I was thinking of starting from scratch because then I could maybe make a metric leadscrew and then i could make a tap if I make the leadscrew a bit longer than needed. The advantage of this is that I could make it so the travel will be what it says on my tailstock dial.
That leads to another question. I am mathimatically challanged ( I am a plumber so I am allowed to be)My dial shows two graduation marks The one is in increments of 0.02mm and the other one is showing .001" Does this confirm its a 10 tpi?

MuellerNick
10-04-2010, 07:50 AM
What confuses me is that it seems to be a strange size.

That shouldn't confuse you!
Friend needed a new nut for his traversal. Ordered it, arrived but didn't fit. Way too tight. He had to order the nut and the spindle. Seems they live 100 years back, when parts were individually fitted.


Nick

JCHannum
10-04-2010, 08:37 AM
I don't think it is as much living 100 years in the past as it is in conversion factors when they clone their machines. 14.35mm is very close to 9/16", like the Chinglish in their literature, I think they also resort to Chimperial for dimensioning.

SGW
10-04-2010, 11:04 AM
What do the dial graduations say for one turn of the leadscrew? If it's 10tpi, the 0.001" dial should come out even with 100 graduations. Or if you put a metric scale on the threads, 50 threads ought to measure 127mm.

I take it you're a metric fan. If that's the case and if the leadscrew is 10tpi, I think I would make both a new leadscrew, to a convenient metric pitch, and a new nut.

CountZero
10-04-2010, 12:03 PM
The chinese are not too picky about accurate graduations....

The Artful Bodger
10-04-2010, 03:46 PM
10 TPI is very close to a metric pitch of 2.5mm.

The Artful Bodger
10-04-2010, 03:48 PM
I was very curious to know if I could do this in acetal and asked if vesconite (a s african invention could be used for this as its self lubricating and doesnt absorb water but apparently its melting point is to high What do you think? Would it stand up to say drilling a 30mm hole in steel. I was thinking of starting from scratch because then I could maybe make a metric leadscrew and then i could make a tap if I make the leadscrew a bit longer than needed. The advantage of this is that I could make it so the travel will be what it says on my tailstock dial.


It is very easy to make the plastic nut if you want to give that a trial.

KiddZimaHater
10-04-2010, 06:12 PM
Adapatap,
Just replace the nut and screw.
I had to do that with my tailstock, since it was missing not only the nut and screw, but also the spindle.
Just drill the nut to accept set-screws, and mount it on the end of the spindle.
Left-Hand Acme Threaded Rods (http://www.mcmaster.com/#acme-threaded-rods-and-studs/=94tqxe)
Acme Nuts (http://www.mcmaster.com/#bronze-general-purpose-acme-nuts/=94trz2)

whitis
10-04-2010, 07:05 PM
Are you measuring the pitch diameters with thread wires (and using the table/math for acme/trapezoidal threads rather than v-threads) or are you measuring the almost irrelevant outside/major diameter? It is the pitch diameter which you need to duplicate accurately (with a little clearance) if you are going to make a replacement that mates with the original lead screw.

Do figure out if it is 2.5mm pitch or 10tpi.

plunger
10-05-2010, 12:43 AM
I am measuring across the threads and over a distance of 25.4mm there are 10threads. I am trying to wrap my head around the maths of advancing 0.02mm as per the grads on my dial. It has two grad wheels . The first is 0.02mm and the other is 0.001" for those confused folks in the states.( dont know how to insert a smilie just yet) I am almost certain that would confirm its a 10 tpi.I wish I had the know how to measure with thread guages and wires but I dont.But if I understand you correctly the pitch determines the travel and the od is absolutely irrelevant. Buying a nut and thread is out of the question as I live in s africa and you guys are real spoilt.

Another question? Could I turn a acme internal cutting toolby using a piece of drill rod and turning the shape of the acme cutting tool by using the compound slide? I found it real hard to free hand grind such a small tool in 4mm piece of round hss