Confused over threading gears

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shepdog
Posts: 51
Joined: Tue Jun 20, 2006 2:21 pm

Confused over threading gears

Post by shepdog » Mon Dec 31, 2012 8:43 pm

I have a craftex busy bee b229 machine, about 6 years old, and trying to cut 11 tpi. Problem is I've got three different sources for what gears to be using.

Chart on machine shows 72-120-127-33

Went to busybee yesterday, new version shows 72-127-33

On line manual shows 72-120-33

...help! :shock:

Torch
Posts: 1561
Joined: Wed Mar 17, 2010 7:58 am
Location: Muskoka

Re: Confused over threading gears

Post by Torch » Mon Dec 31, 2012 10:34 pm

The Craftex machines may be supplied with metric or inch lead screws, depending on the age. The factory could supply either 6tpi or 4mm and BusyBee ordered different versions at different times. There may well be other variations in the headstock gearing, but I have no knowledge of that.

Based on your machine's chart, I would bet your machine has a metric lead screw -- the key being the 120:127 ratio. If cutting an inch thread on a machine equipped with an inch pitch lead screw, then the middle gear makes no difference -- you could use any gear without effect on the final ratio because the gear is just being used as an idler, both the driving gear and the driven gear are riding the same intermediary. The 120:127 pair DOES change the ratio between the input and the output and is the required ratio between metric and inch, speeding up the output gear slightly. (Similarly, cutting a metric thread on an inch leadscrew requires the same gear pair, just inversed: 127:120)

I would go by the chart on your machine and run a test. Very lightly scratch the surface of a piece (any piece, any diameter) with the thread form tool with the machine set up at 72-120-127-33 (and the levers set appropriately, of course -- eg: if the headstock lever is supposed to be set at "II" but you set it at "III" you would probably end up with 22tpi instead of 11). Then use a thread pitch gauge or a sample bolt with known thread to check the pitch.

EDIT:
If you've already tried all that, then maybe the wrong chart was installed. You could always measure the leadscrew to verify the pitch. If you don't have a thread pitch gauge that course, count 10 threads and measure. If the distance between 10 threads is 40mm, then you have a metric leadscrew. If the distance is 1.667" (42.33mm) then you have an inch leadscrew.

shepdog
Posts: 51
Joined: Tue Jun 20, 2006 2:21 pm

Re: Confused over threading gears

Post by shepdog » Tue Jan 01, 2013 12:09 am

THANK YOU! This, I understand finally!

I ran it as you suggested tonight, but need a lot of work getting a clean thread. Seems like backlash in the cross slide resetting it to zero is creating some error, going to try with a hard stop clamped to the table tomorrow.

Torch
Posts: 1561
Joined: Wed Mar 17, 2010 7:58 am
Location: Muskoka

Re: Confused over threading gears

Post by Torch » Tue Jan 01, 2013 3:43 am

Ahhhh, the pursuit of clean threads...

First, verify which way the angle on the compound is marked. Some lathes have it marked such that "0°" is when the top slide will move perpendicular to the work piece (ie: same direction as the cross slide). In this case, you want it set to about 29° to 29-1/2°. Other lathes have it marked so that "0°" is when the top slide moves parallel to the work (ie: same direction as the table). In this case, you want it set to about 60-1/2° to 61°. Harold suggests thinking of it as a clock: looking down on the lathe, 12 o'clock is directly away from you and the handle of your cross-slide should be at about 5:00.

Using the compound to feed for all but the last pass or so will ensure you are cutting with the leading edge of the tool and help keep the threads clean.

Next step is to make sure the tool bit is ground exactly 60°. It shouldn't come to a sharp point -- there should be a tiny flat on the end. Ideally, the flat should be a precise width for the pitch, but personally I cheat a bit. I have a couple of threading bits ground to cover a range of pitches. I'll use the one that doesn't have too wide a flat.

With the bit mounted in your tool post, adjust the tool post angle so the angle exactly bisects a line perpendicular to the work. I cheat a bit when grinding the bits -- I have an optical comparator so I can ensure the angle is symetrical. However, it's easy to grind the angle off-square a touch. Put the notch on the side of your fish-tail (you do have a 60° fish-tale, right?) on the tool bit and make sure the body of the fish-tale is parallel to the work. Once that is all set, lock down the tool holder. Make sure the tool bit is on-centre vertically.

Once everything is squared up, you can set your depths. What I do is clean off the jaws of the vise and close the compound fully. Then I run the tool bit in, pinching a piece of cigarette rolling paper between the bit and the work. When the paper just grabs, I'm there. Then I set the cross-slide DRO axis to the diameter of the work piece. At this point, I will turn my stop groove to depth, if appropriate. Otherwise, I wind out the compound and wind in the cross-slide to my final depth, less about 0.005" (diameter -- that's about 2.5 thou of actual feed) for my final passes. Finally, I use the compound to pinch the cigarette paper again and set the compound dial to 0 before backing it off a touch again.

Then I line up the table to start cutting the thread. Note that if you are using the 120:127 gear set (ie: cutting inch threads with a metric lead screw or vice-versa) YOU CANNOT USE THE THREAD DIAL. You will have to reverse the machine between each pass. I mention this now because reversing the machine puts a different load on the change gears -- instead of drawing themselves together, they want to push apart. Make bloody sure you have the change gear bracket bolts nice and tight because if they push apart and skip a tooth or three, you will make a mess of your thread on the next pass! Don't Ask Me How I Know This (TM).

Ok, with the table in position, bring the compound in to about 1 thou, pick a number on the thread dial, and engage. I find 100 - 125 rpm is usually just about right for threading. Any faster than that and I have trouble stopping the motor at the right moment to avoid over-running my stop groove. The lathe will continue to turn a bit when you kill the motor, so it's a matter of timing. At the end of the pass, wind the compound out past 0, so the bit will clear the threads, reverse the motor and take the table back well past the start of your thread. Now is a good time to check the thread pitch before it's too late. Again: DAMHIKT (TM).

I use the compound to feed in for each pass. The first couple of passes I might feed the compound 5 thou. The last few I feed at 2-1/2 thou per pass. It's not really cutting that deep because of the angle, of course. Once the vice has closed and I'm back to my starting point, it's time to clean up the edges by feeding in the cross-slide about 0.002" (diameter -- that's 1 thou of actual infeed). If I have a nut I'm working to, I'll try it at this point. If my measurements were right, it should be too tight to wind on. But, if I screwed up and cut deeper than I realized, I might be done already. If I don't have a nut, then I get out the thread wires for some careful measurements.

Usually, I need one more pass. However, if my bit was too pointy, then I may need a few more. Again, I try to keep them light, 2 or 3 thou.

As for dealing with backlash, all machines have it. Just make sure you always wind things off further than you have to, then wind in to your mark. If you wind out and cut, then the table/compound/cross-slide can move away from the work and cause errors.
Last edited by Torch on Tue Jan 01, 2013 8:53 am, edited 1 time in total.

Harold_V
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Re: Confused over threading gears

Post by Harold_V » Tue Jan 01, 2013 4:47 am

Well done, Torch!

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.

Torch
Posts: 1561
Joined: Wed Mar 17, 2010 7:58 am
Location: Muskoka

Re: Confused over threading gears

Post by Torch » Tue Jan 01, 2013 8:51 am

Aw shucks, it was nothing. All I had to do was think of every mistake I made while learning and then write down what you and Jose and Glenn, et. al. told me to do to fix it. :lol:

shepdog
Posts: 51
Joined: Tue Jun 20, 2006 2:21 pm

Re: Confused over threading gears

Post by shepdog » Tue Jan 01, 2013 5:36 pm

"YOU CANNOT USE THE THREADING DIAL."

:shock:


WELL, WHAT THE #}{#~%! Do they put it there for....!?!?!

:cry:

Followed your directions to a T, made a perfect thread in some aluminum. Tried on the steel, all went to crap. My machine simply is piece of crap, way too sloppy in the feed,etc.

But that first sentence above was like discovering fire....thank you so much!

Torch
Posts: 1561
Joined: Wed Mar 17, 2010 7:58 am
Location: Muskoka

Re: Confused over threading gears

Post by Torch » Tue Jan 01, 2013 9:13 pm

Obviously you are in Canada. Any chance you are somewhere between the GTA and Muskoka? I could possibly stop by one day and have a look.

In the meantime, you should make sure your gibs are properly adjusted to avoid any rotational motion. Get some decent way oil to minimize stiction. Ensure the tool post is mounted as rigidly as possible. Feeds screws alone should not cause problems -- as I said, all machines have some backlash and you simply allow for that by always winding out past your mark then in towards the mark so the screw is preventing things from changing. It sounds to me like something else is sloppy and giving you grief. I have a very similar machine (made in the same factory as yours) and I can thread aluminium, brass, steel, stainless steel, etc. using the above technique. Oh, and some cutting oil. I don't think I mentioned that before: make sure you use cutting oil on steel. You can get a quart bottle at Home Depot or other plumbing supply, if nothing else is available. Kerosene or even WD-40 is adequate for aluminium.

Torch
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Joined: Wed Mar 17, 2010 7:58 am
Location: Muskoka

Re: Confused over threading gears

Post by Torch » Tue Jan 01, 2013 9:59 pm

Of course, there's steel and then there's steel. What kind of steel are you threading? Some steels don't like to leave a nice finish and are tricky even with lots of practice. 12L14 or 1144 stressproof are great for threading. O1 tool steel and 4140 prehard seem to take a pretty nice thread too. Stuff like 1018 or 1040: not so much.

That's not to say it can't be done. I had to make a 3/16" shaft 8" long today. At hand was a piece of mystery metal. It was a good thing it started off 3/8" because it took many passes to figure out the right combination of speed and feed rate to get an acceptable (not good, just acceptable) finish for the job at hand.

shepdog
Posts: 51
Joined: Tue Jun 20, 2006 2:21 pm

Re: Confused over threading gears

Post by shepdog » Tue Jan 01, 2013 10:15 pm

I'm just pouting, lol.. :D appreciate the offer, but I'm in Burlington...


The play seems to be coming from the leadscrew engagement lever on the left....going back and forth on the direction, it seems to be coming loose , as in not staying engaged. Going to have to take it apart I think.

While we're on the topic, what ther tweaks should I be checking to "tighten up" my machine? I got it at their tent sale for only 500 bucks so it certainly doesn't owe me much, it's been great for turning spacers, etc. but am having trouble seeing getting much more danced with it unless I get it working better.

Torch
Posts: 1561
Joined: Wed Mar 17, 2010 7:58 am
Location: Muskoka

Re: Confused over threading gears

Post by Torch » Tue Jan 01, 2013 10:39 pm

shepdog wrote:I'm just pouting, lol.. :D appreciate the offer, but I'm in Burlington...


I won't be down that far for another month. Too bad we didn't have this conversation on Friday -- I drove through Burlington this past Saturday morning. Oh well...
The play seems to be coming from the leadscrew engagement lever on the left....going back and forth on the direction, it seems to be coming loose , as in not staying engaged. Going to have to take it apart I think.

While we're on the topic, what ther tweaks should I be checking to "tighten up" my machine? I got it at their tent sale for only 500 bucks so it certainly doesn't owe me much, it's been great for turning spacers, etc. but am having trouble seeing getting much more danced with it unless I get it working better.
Well one of the things I did was to remove both the lead screw and the cross-slide screw to touch up the edges of the threads at the slot. I think they cut the slot after the threads and the edge was wearing away at the brass half-nut. (One of these days I'm going to make a bronze half-nut). And yes, when the half-nut was well-worn, it didn't want to stay engaged, especially in reverse. I had to keep my hand on the lever and apply a little upward force when feeding away from the head.

Another mod I made was to extend the table gib screws. Now they sit out front and are secured with lock-nuts instead of that stupid double-screw system. Much easier to adjust this way. I replaced the stock tool post with a QCTP, and made a base plate to centre it on the table. I think that aids in stability somewhat.

Most of my other lathe mods would not be directly applicable to you because of differences between our machines.

shepdog
Posts: 51
Joined: Tue Jun 20, 2006 2:21 pm

Re: Confused over threading gears

Post by shepdog » Tue Jan 01, 2013 10:53 pm

It's actually the other lever, the one that actually turns the leadscrew...there's a pair of crown nuts that engage each other...I suspect they may be on their way out.

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