Metric transposing gears on early Heavy 10

[kitno455]

Let's return to the question Roger posted. Roger, I assume you have the normal 24 tooth stud gear, 66 tooth gearbox input gear, and the 4 to 224 TPI gearbox. Given that the gears on the banjo have a fixed center distance, your only simple choice is to swap the stud gear. If you replace the 24 with a 34, you will turn the leadscrew at 1.417 times its normal speed. This will make the leadscrew act like it is 5.647 TPI, which is 4.498 mm pitch. Given the ratios in the box, that will enable you to cut 12 common metric pitches with only .047% error:

TPI MMPT %ERR
144 0.25 0.047
80 0.45 0.047
72 0.50 0.047
48 0.75 0.047
40 0.90 0.047
36 1.00 0.047
24 1.50 0.047
18 2.00 0.047
12 3.00 0.047
9 4.00 0.047
8 4.50 0.047
6 6.00 0.047

That's close enough that it will be masked by the wear in your leadscrew, and would suit most uses.

If you instead use a 33 tooth stud gear, the leadscrew is like 5.82 TPI (4.37mm), enabling 5 more pitches with somewhat worse error (.214%)

TPI MMPT %ERR
28 1.25 0.214
20 1.75 0.214
14 2.49 0.214
10 3.49 0.214
7 4.99 0.214

These are likely good enough for general fastener use. If you'd rather have lower % Error on those pitches, you'll need a two gears instead.

With a 38 tooth stud gear:

TPI MMPT %ERR
23 1.75 0.082
11.5 3.50 0.082

With a 26 tooth stud gear:

TPI MMPT %ERR
22 1.25 0.061
11 2.50 0.061
5.5 5.00 0.061
5 5.50 0.061

Check the pitch of your existing gears. I expect they are 18DP, 14.5 PA (like the 9" workshop), but .5" face width instead of .375". Anything you use will have to match.

Hope this helps!
allan

 

[kitno455]

Oh, and if you do decide to use a compound gear instead, here is a neat way to do it: Metric transposing gear for single tumbler heavy 10

 

[mattthemuppet]

I think it was kitno455 posting that info in another thread that got me wrangling an Excel spreadsheet to figure out what he already posted With a 33 and a 34t tumbler gear (the bottom most one that meshes with the top gear on the banjo) and using the half nuts or the feed selector you can get all metric pitches from 3mm down (didn't look for larger than that) with errors ranging from 0.046 to 1.13% depending on the pitch.

I'll most likely be 3D printing the gears (sorry chaps) as I don't currently have the means to cut gears. If anyone wants the spreadsheet feel free to PM me your email and I'll send it over. If I could figure out how to attach it here I would!

Zahnrad Kopf - that might be something that there's a market for. Probably not a huge one, but then I don't know how much cost and effort it takes to knock a few sets of these out.

 

[kitno455]

If someone is looking to go into production on something, my suggestion is a 63 tooth gear in each of the DP and face width combos needed for SB lathes. They can be married to the outside of the 80 tooth idler on all the double tumbler machines, and the loose change gear machines came with an 80 tooth gear that could be pressed into service as a compound with a keyed bushing.

allan

 

[Roger Best]

That's terrific Allan,

I will check the details of the gears. It's a safe assumption that they are standard.

 

[Peter.]

Let's return to the question Roger posted. Roger, I assume you have the normal 24 tooth stud gear, 66 tooth gearbox input gear, and the 4 to 224 TPI gearbox. Given that the gears on the banjo have a fixed center distance, your only simple choice is to swap the stud gear. If you replace the 24 with a 34, you will turn the leadscrew at 1.417 times its normal speed. This will make the leadscrew act like it is 5.647 TPI, which is 4.498 mm pitch. Given the ratios in the box, that will enable you to cut 12 common metric pitches with only .047% error:

TPI MMPT %ERR
144 0.25 0.047
80 0.45 0.047
72 0.50 0.047
48 0.75 0.047
40 0.90 0.047
36 1.00 0.047
24 1.50 0.047
18 2.00 0.047
12 3.00 0.047
9 4.00 0.047
8 4.50 0.047
6 6.00 0.047

That's close enough that it will be masked by the wear in your leadscrew, and would suit most uses.

If you instead use a 33 tooth stud gear, the leadscrew is like 5.82 TPI (4.37mm), enabling 5 more pitches with somewhat worse error (.214%)

TPI MMPT %ERR
28 1.25 0.214
20 1.75 0.214
14 2.49 0.214
10 3.49 0.214
7 4.99 0.214

These are likely good enough for general fastener use. If you'd rather have lower % Error on those pitches, you'll need a two gears instead.

With a 38 tooth stud gear:

TPI MMPT %ERR
23 1.75 0.082
11.5 3.50 0.082

With a 26 tooth stud gear:

TPI MMPT %ERR
22 1.25 0.061
11 2.50 0.061
5.5 5.00 0.061
5 5.50 0.061

Check the pitch of your existing gears. I expect they are 18DP, 14.5 PA (like the 9" workshop), but .5" face width instead of .375". Anything you use will have to match.

Hope this helps!
allan

That's great Allan, thanks. It will cover most every common fastener pitch with a small enough error for fasteners for sure. Much less trouble than swapping banjos. It's a shame that there's no solution for 0.8 0.7 and 0.6, that would really cover it all. 0.8 especially is standard pitch for M5.

 

[Roger Best]

I see that on the original SB diagram, using a 127/100, gear, that those pitches require three different stud gears and its not the ones above.

I feel a table for my workshop notice board coming on.

 

[mattthemuppet]

That's great Allan, thanks. It will cover most every common fastener pitch with a small enough error for fasteners for sure. Much less trouble than swapping banjos. It's a shame that there's no solution for 0.8 0.7 and 0.6, that would really cover it all. 0.8 especially is standard pitch for M5.

It's worth pointing out that all the pitches Allan worked out are using the carriage feed, not the half nuts. With the half nuts and the 34t tumbler gear you can get 0.8 and 0.7 with -1.16% error. With the 33t tumbler and half nuts you can get 0.6 with a -0.5% error and using the carriage feed you get 0.8 with -0.79% error. I'm going to have to print these out and laminate them as there's no way I'm remembering this stuff.

Allan - there's a small error in your 34t calculations - the ratio change is 1.41176 (not 1.417) so the error is actually lower at -0.046%

 

[Zahnrad Kopf]

Zahnrad Kopf - that might be something that there's a market for. Probably not a huge one, but then I don't know how much cost and effort it takes to knock a few sets of these out.

This is another one of those projects that is more about helping out than it is about viable products. I don't expect that very many of them will sell, but I have a small running list of people that have stated that they want them once we complete them. We have been making the 127T/100T compound gears for various machines, for some time now. I'd been meaning to make the SouthBend ones for some time, but there was always something that would pop up and get in the way. During the holiday season, I simply decided to take an opportunity to finally do it after a couple of people asked me about them within the span of a week. It'll likely saturate the market for the foreseeable future with just a handful. LOL.

 

[Peter.]

It's worth pointing out that all the pitches Allan worked out are using the carriage feed, not the half nuts.

You sure about that? Selecting 8tpi on the gearbox but using a 34 tooth input yields 8*24/34=5.647tpi, or 4.498mm pitch as per Allan's post - on the leadscrew and half-nuts.

I wouldn't be interested in any solution that involved cutting threads via the rack feed.

 

[Roger Best]

I can confirm that my lathe, and very presumably Peters has 18DP gears.
The stud gear is 1/2" wide, but the speed-change gears are only 3/8". The gearbox input is 1.16" so plenty wide enough.
Gearbox is 4-224, as described

The gear carrier has a huge adjustment, so I am sure it is intended for using a variety of change gears. Is that because it is common with simpler machines?

 

[mattthemuppet]

This is another one of those projects that is more about helping out than it is about viable products. I don't expect that very many of them will sell, but I have a small running list of people that have stated that they want them once we complete them. We have been making the 127T/100T compound gears for various machines, for some time now. I'd been meaning to make the SouthBend ones for some time, but there was always something that would pop up and get in the way. During the holiday season, I simply decided to take an opportunity to finally do it after a couple of people asked me about them within the span of a week. It'll likely saturate the market for the foreseeable future with just a handful. LOL.

I totally understand and we're lucky to have you!

You sure about that? Selecting 8tpi on the gearbox but using a 34 tooth input yields 8*24/34=5.647tpi, or 4.498mm pitch as per Allan's post - on the leadscrew and half-nuts.

I wouldn't be interested in any solution that involved cutting threads via the rack feed.

ooh, that's embarrassing on two counts. I worked out mine starting with the 48t tumbler that comes on my lathe (it can cut 2tpi as stock for some reason) which gives 1.4118 vs. 1.417 with a 24t tumbler. All of the threads on my wide 9 are 1/2 that for other single tumbler SB gear boxes at the same position. I also looked in the wrong column - you and ALlan are right, all of the pitches Allan calculated are using the halfnuts.

Why the objection to using carriage feed vs. halfnuts? Both use the lead screw and most people do metric threading on imperial lathes by stopping and reversing the motor rather than opening the halfnuts. They should be equivalent in accuracy (bar any gear wear) and ease, as far as I can see.

 

[Peter.]

Why the objection to using carriage feed vs. halfnuts? Both use the lead screw and most people do metric threading on imperial lathes by stopping and reversing the motor rather than opening the halfnuts. They should be equivalent in accuracy (bar any gear wear) and ease, as far as I can see.

First and foremost if the apron clutch slips you'll trash your part. Apart from that you lose the ability to thread to a shoulder using the oxtools method. Mostly though it just feels wrong to be turning a thread with the rack feed.

 

[kitno455]

matt- You cannot thread with the longitudinal feed because of clutch slippage. The rack is also not nearly as precise as the leadscrew.

Also, the early single tumbler machines turned the gearbox twice as fast as the later machines, and hence did not have as fine feeds, but did have a row of coarser threads. I would probably upgrade such a machine to the later configuration with a stud gear swap.

allan

 

[kitno455]

We actually can pick up a few more threads with a couple more gears:

With a 25 tooth stud:

TPI MMPT %ERR
88 0.30 0.222
44 0.60 0.222

With a 37 tooth stud:

TPI MMPT %ERR
112 0.35 0.106
56 0.70 0.106

Those have slightly worse error than I would like, but should be fine for fasteners. Unfortunately, .8mm seems elusive. I'll poke around for other options.

I suppose I could look around for BA threads as well, but I dunno why anyone would want to use those goofy things

allan

 

[Peter.]

I suppose I could look around for BA threads as well, but I dunno why anyone would want to use those goofy things

allan

0BA and 1Ba already catered for. 2BA within 0.01mm/pitch if there's a solution for 0.8mm. Most of the others are good enough that you could part-cut them then finish with a die to prevent drunken threads.

 

[mattthemuppet]

First and foremost if the apron clutch slips you'll trash your part. Apart from that you lose the ability to thread to a shoulder using the oxtools method. Mostly though it just feels wrong to be turning a thread with the rack feed.

fair enough. You'll need to do the math to find a 0.6 pitch then

matt- You cannot thread with the longitudinal feed because of clutch slippage. The rack is also not nearly as precise as the leadscrew.

Also, the early single tumbler machines turned the gearbox twice as fast as the later machines, and hence did not have as fine feeds, but did have a row of coarser threads. I would probably upgrade such a machine to the later configuration with a stud gear swap.

allan

I didn't realise the clutch would slip that much, though I can see that if it did that would screw up the part instantly.

I'll be replacing the 48t tumbler gear with a 24t as soon as I can. If for no other reason that the finest feed is still fairly coarse with the 48t.

 

[Roger Best]

That's great news Zahnrad, I am sure steel is better than 3D printed, although this one looks promising:

100/127T Boxford lathe conversion gear | eBay
He also does a set of gears for £70, pretty cheap, almost disposable.

The method of mounting is pretty important. I am watching Peter's progress closely.
Here is another chap who manages with just a few gears, thanks for the link that led to it:
Metric transposing gear for single tumbler heavy 10

To answer Peters question, I may well want to use BA threads, they are useful for small linkages, you never know what will turn up in the next 30 years, or what a subsequent owner might do in the next 130 years.

I have looked at the numbers for BA threads - they are weird and may have to be ignored.

 

[SLK001]

Why the objection to using carriage feed vs. halfnuts? Both use the lead screw and most people do metric threading on imperial lathes by stopping and reversing the motor rather than opening the halfnuts. They should be equivalent in accuracy (bar any gear wear) and ease, as far as I can see.

You can't thread using the carriage feed clutch (to specific standards anyway), because the feeds are different. If you look at your gearbox thread chart, you will see numbers for the TPI and the feeds. They are NOT reciprocals of each other. For example, on a 10L chart, the setting for a 10TPI thread has a feed rate of 0.0334" per revolution (instead of 0.100" that would be the correct reciprocal).

 

[mattthemuppet]

I get that, you'd have to work out the pitch taking into account the 3.5x (or something similary) factor of the carriage feed vs. halfnuts. I did that and found a few extra metric pitches that can be cut, but Peter and Allan's explanation of why one shouldn't makes complete sense to me.