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 thread.
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.
Unka' George ================ When we are planning for posterity, we ought to remember that virtue is not hereditary. Thomas Paine (1737-1809), Anglo-American political theorist, writer. Common Sense, ch. 4 (1776).
The Home Machinist issue May/June 2007 has a great article on how to cut threads without the correct gearing. "Expanding Thread Cutting Options on Lathes with Quick-change Gears" by Kim Steiner Try your news stand.
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 trick.
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 to tap.
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.
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 approximations. 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
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.
47/37=1.2702 accurate enough for nearly everybody, and It fits inside the lathe.
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.