I just purchased a small prazi (basically to convert to cnc, during
shipping the cross feed dial snapped off. Long story short, I need to
thread a 10 x 1.5 mm bolt. I have a 13x40 clausing Colchester and
have the following gears 20,21,57,66,69,7278 and 80. can anyone
explain how I can accomplish this? I imagine I need a new gear (I can
try to make this myself I guess, Clausing charges 1 billion dollars
for there splined gears) but am just having a brain cramp as far as
figuring out how i need to arrange gears to get the right ratio. Any
help would be greatly appreciated.
Yep, but, the threaded bolt is on the dial end of a threaded lead
screw that moves the cross feed and wanted to try and figure out how
to make the metric thread. But, in the name of progress, your right I
could figure that out in the calm of another day. That begs the
question, can I cut a thread through tool steel (pre hardened of
course) with a simple tap and die set? I have never threaded a raw
stock without a lathe, I occasionally use the tap and die set to clean-
up threads. I also wonder how I would hold the non-business end of
the part while putting the large amount of force needed to cut the
Why are you making a screw from pre-hardened tool steel?
Seems to me you could make the screw from leaded brass and it would do the
If you want go ahead and use a drill blank to make your screw. and that you
can thread with a die just fine. If you really need it hard, you can harden
it after you cut the threads.
Cutting threads on hardened steel is best done by a thread grinder.
I have never threaded a raw
There are several ways to do it. First of all you could stick it in a vice
and use the die in the die stock. Not much different than the force needed
Another way to thread is to make your screw a little long and give the end a
lead (taper). Start the die square by removing the chuck or center from the
tail stock and butting up the end of the tail stock shaft to the die.
Grab the three jaw chuck and turn it slowly to you while holding the die
stock. Advance the tail stock to keep it square until you get a few threads
cut. now you can use the lathe to do the pushing if you want (Slow speed,
lots of cutting oil.) or just continue turning the chuck by hand. You can
also set the cross slide to grab the end of the die stock.
If you have a small lathe chuck you can cheat a bit and use the chuck wrench
for additional leverage.
You will get the best thread quality if you use sufficient oil and back off
the die to break the chips.
About the time I had mastered getting the toothpaste back in the tube, then
Click this link to clear the brain cramp It is exactly on topic. It
even talks about your 1.5 mm thread.
I don't know if this will work for you
I bought the 37 and 47 tooth gear blanks from Scott logan and then fit them
into my 10EE. Now with a gear change, i can cut any metric thread on an
imperial machine. I think this can be done, with some thought, on any lathe.
Unfortunately its not that simple. Firstly, in order to precisely
convert between metric and Imperial threads you need a 127 toothed gear
somewhere in the train - your 37 and 47 toothed gears will only give you
Secondly, the thread pitches cut on an Imperial gearbox equipped lathe
are in fixed ratio groups. On my lathe, for example, I have 8 starting
ratios (4, 4.5, 4.75, 5, 5.5, 6, 6.5, and 7 TPI) and for each of those
the gearbox can multiply them by the 5 fixed ratios of 1, 2, 4, 8 and
16. This gives 40 different TPIs in 8 groups of 5, giving TPIs from 4 to
112. EG. the 4th group, has a starting TPI of 5 and thus gives TPIs of
5, 10, 20, 40, and 80.
When you look carefully at the metric pitches you will notice that they
fit into a different fixed ratio pattern. The 24 common pitches from
0.25mm to 5.0mm can be conveniently obtained from the fixed ratios of 1,
2, 5 and 10, and the starting pitches of 0.25, 0.3, 0.35, 0.4, 0.45 and
0.5. Because of the different fixed ratios, you cannot simply insert a
127 tooth gear somewhere and expect to cut all the metric threads from
an Imperial leadscrew and gearbox.
Some time ago I bought a 127 tooth gear and decided to investigate what
other gears would be needed to cut all the common metric threads from
0.25mm to 5.5mm. I wrote a program that took into consideration the
gears that I could buy that would mesh with the 127 I already had. It
ended up with 25, 30, 55, 63, 65, and 75.
I hope this helps.
Regards, Gary Wooding
(To reply by email, change feet to foot in my address)
47/37=1.2702 accurate enough for nearly everybody, and It fits inside the
I can only speak for my Monarch 10EE and my Leblond. Both these machines
have levers to move for different thread pitches. And both machines have a
gear train at the left end of the tail stock for ranges of thread pitches
and feeds. This is where you swap out for the 47 and 37 tooth gears.
Scott Logan goes into considerable detail on his web site to explain how to
accomplish metric threading on machines with loose change gears.