# screw cutting on sieg mini lathe. HELP



## bazmak (Oct 30, 2013)

Hi everybody,im hoping someone can help/advise me
Can i cut a 10tpi thread. 2.5 pitch should be OK
The chart on the mini lathe only goes to 2mm pitch
If possible what would be the gear chain.Any help/comments would be
much appreciated. Regards barry


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## Tin Falcon (Oct 30, 2013)

Yes you can get very close.
these charts are assuming a 1.5 mm lead screw found in most parts of the world  most US minis have a 16 tpi screw so the numbers would be different. but the link will help in any case. 

http://littlemachineshop.com/Reference/change_gears.php

Change Gear Results

7x10, 7x12, 7x14, 7x16 Mini Lathe - 10 TPI thread pitch
Lathe settings are at the bottom of this page.

A	B	C	D	Thread Pitch	Percent Error	Error in 1" of Thread
55	20	40	65	10.006 TPI	0.061%	0.0006 in
55	65	80	40	10.006 TPI	0.061%	0.0006 in
80	40	55	65	10.006 TPI	0.061%	0.0006 in
Instructions

There are 4 positions for the change gears, commonly called A, B, C, and D.

A	This is the top change gear position. When you received your lathe it had a 20-tooth metal gear in this position.
B	Gear positions B and C are on the same shaft, between positions A and D. Position B is the inside gear on this shaft. When you received your lathe it had an 80-tooth plastic gear in this position.
C	Gear positions B and C are on the same shaft; between positions A and D. Position C is the outside gear on this shaft. When you received your lathe it had a 20-tooth metal gear in this position.
D	Position D is the end of the lead screw. When you received your lathe it had an 80-tooth plastic gear in this position.


Info from littlemachinineshop.com 



Hope this helps.
Tin


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## bazmak (Oct 30, 2013)

Many thanks for your prompt reply Tin.Will attempt my first single point
screw cutting in 20 years. I have just bought a small Advance lathe on e-bay
and have stripped it down,refurbished and reassembled.The nose is threaded
1" BSF (supposidly) 55o W form x 10tpi.I bought a 1" bsf nut but locks up,not sure yet where the problem is.I need to make,adaptor plt and faceplt for mounting chucks etc.Will 1st attempt a male thread,its easier and if thats 
successfull wil then try internal screwcutting.Any advise.I assume compound set at 27.5o.How do i locate each pass without a thread dial indicator.If possible could you let me have a list of additional threads that can be cut with the supplied gears.Many thanks
Regards barry


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## Tin Falcon (Oct 31, 2013)

Barry :

If you do not have a thread dial you will need to keep the half nut engaged .
(that is unless the thread is an even multiple of the lead screw) 

SOOO here is some info that should help a lot . Download it print it put it in a note book paper the shop wall with it if needed but read it understand it and use it. 
first of all the manual that should have come with your mini ,lathe but did not.

http://littlemachineshop.com/Info/MiniLatheUsersGuide.pdf

second of all a threading guide written for mach 3 cnc threading. before you or anyone else throws up arms and says but I am manual threading not using cnc read the manual. yes there are many pages you will ignore if not using mach 3 but there is a heap of threading info applicable to ALL lathe threading. 




http://www.machsupport.com/wp-content/uploads/2013/02/Mach3_Threading.pdf



And yes you will need to do a male thread first because you will need a male thread to gauge the size of the female thread. 


Littlemachineshop ,com can sell you a thread dial or any other part for the SIEG.
If you use the link in the previous thread you should be able to figure out the gears for any or almost any thread. you may need to get a 21 tooth gear to do imperial threads since you have a metric lathe. 
Tin


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## bazmak (Nov 14, 2013)

Hi again Tim,many thanks for your advise.After much head scratching
and recovering latent memories i finally worked out the basic formula
55/20 x 40/65 x 1.5 p = 2.54 pitch simples.Unfortunately the lathe did not come
with the 55 or 65 tooth gears.With the gears supplied i could get
60/40x40/35 x 1.5 = 2.57 Near enough for now thought i.Wrong .the gear train falls short of the leadscrew. Need the larger gears.Any advise where i can obtain the additional gears? Regards barry


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## hi speed scrap (Nov 15, 2013)

Hi Barry,

Try here,

http://compare.ebay.com.au/like/390697474242?clk_rvr_id=548079712696

here,

http://www.machines4u.com.au/browse/Metalworking-Machinery/Lathe-36/Bench-Top-Lathes-678/Melbourne/

or here,

http://www.machineryhouse.com.au/Centre-Lathes

Dave


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## Tin Falcon (Nov 15, 2013)

Here in the US the typical suspects are 
http://littlemachineshop.com/

These guys specialize in parts and accessories for the small machines and they now sell small machines. 
PLug your gear numbers into there gear calculator see what it comes up with. 

http://www.micromark.com/
Is in new jersey they sell machines some accessories they are a hobby tool company machine tools is part of there offering

Tin


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## Tin Falcon (Nov 15, 2013)

http://thehobbyistmachinestore.com/store/Mini-Lathe-Change-Gears.html

Have not dealt with this guy but has steel change gears sets for $55 that is 45% less than LMS

Tin


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## bazmak (Nov 18, 2013)

Thanks Tin,i have ordered a set of gears from hobbyist machine stores.$55 + $36 postage Will keep you posted when they 
arrive,and see if i can do some screwcutting


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## bazmak (Sep 12, 2014)

Hi everybody,back again.My next project is an er32 collet chuck for the Sieg
which i will post as it goes.My question is this.Has anyone done screwcutting on the Sieg variable speed lathe ??? My first attempt was a failure,no thread dial
and the Vspeed is no good,cant keep a low speed/torque,the motor just bogs down.Really need gearbox/backgears etc.However here is my line of thought
PLEASE add comments/suggestions before i get too far.I have fitted a rubbertyred wheel to the back of the headstock and plan to handfeed with the halfnuts permanently engaged and reverse motor back to start. Thread is 40mm
x 1.5 pitch.Will feed in with the compound at 30o etc etc. Last attempt was partially successful but i think the gears jumped a tooth so will have to take more care.I plan to turn the undercut after the thread as i wont have tool overun and this will allow me to cut the thread long.If i damage the first few
threads i can face off the end and have a 2nd bite of the pie.IF ANYBODY HAS
DONE SCREWCUTTING ON THE SC2 PLEASE POST Regards Barry


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## Cogsy (Sep 12, 2014)

I have cut many small threads on the SC3 variable speed (which I believe is almost identical to the SC2 just longer), from 3x0.5 up to about 12x1.25 (could be wrong on the pitch, haven't done it in a while), without any issues. For the small threads, taking around 0.004" per pass, I typically spin the lathe at around 40-60 rpm. With such a small cut depth and a sharp HSS cutter, torque wasn't a problem.

For critical threads, like when I'm making spark plugs, I always cut them on the lathe then clean them with a die, so I can be sure the threads are straight. I now have a slightly bigger lathe, making the SC3 a bit redundant, but I've kept it just for threading because I can turn the speed down so slow.

Without a thread dial I engage the half nut and leave it engaged, withdraw the tool at the end of the cut and reverse the lathe to the beginning of the thread and make my next pass.

Good luck!


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## bazmak (Sep 13, 2014)

Many thanks good to know it can be done will see what ni can do
regards barry


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## bazmak (Sep 15, 2014)

Screwcutting successful.Described on new thread for ER32 collet chuck
Many thanks Bazmak


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