algoa (hemmingway) gearbox change gears

[Ronald HertogParticipant @ronaldhertog38923]

Hi all,

Ive found a diamond in the rough. Having made up my mind i wanted a quick change gearbox for my Myford ML7 lathe. I spotted one on ebay and won the bidding war.

It did require some work, the seller mentioned it so not a problem there. I tore the whole thing apart, carefully taking photographs and laying out the order of components so getting it together would be possible without mistakes. Made a new outgoing drive axle for it and replaced the bearings for a fresh set. Then reversed the teardown and it spins like a charm again.

Now my question, the gearbox didn't come with any documentation. I did bit of research on the web and found the drawings on the Hemmingway webste. Amongst these drawing is a chart wich you can use to cut metric thread using different change wheels assemblies.

I followed the chart and set up for a 2mm pitch. The pitch came out short, i think its more like 1.8 in stead of the 2mm required.

The change wheel set up whas for a couple of pitches, tried them out and they all come up short. The set up i used is. 45, 40/21 idle 50, 75.

I thought, okay so ive made a mistake in the change wheel set up. Re-checked it and compared it to the chart given by hemmingway. I made no mistakes there. So i'm starting to question whether the is a mistake in the chart.

Has anyone experienced the same problems, or is there a mistake ive made wich i can't put my finger on yet?

Edited By Ronald Hertog on 05/11/2017 19:00:37

[Ronald HertogParticipant @ronaldhertog38923]

[Neil WyattModerator @neilwyatt]

Is it possible that your lathe has a metric 3mm leadscrew instead of 8tpi?

[Chris TriceParticipant @christrice43267]

What Neil said.

[DMRParticipant @dmr]

Hi Ronald, The Algoa gearbox is nothing like the Myford one internally or externally and is kit built as you have found. You will need someone who has built the Algoa version to help you unless Neil and Chris have already landed on the answer. I did type into Google "algoa+gearbox" and came up with the following great long link (copy/pasted so it is right). About 2/3rds down is a fair bit on the device.

https://books.google.co.uk/books?id=gZLuDQAAQBAJ&pg=PA9-IA3&lpg=PA9-IA3&dq=algoa%2Bgearbox&source=bl&ots=iwHODqB6oZ&sig=OQa_A8qdLpdCmblSphcvVscZ58s&hl=en&sa=X&ved=0ahUKEwjK56D3z6jXAhVGIMAKHSFCDtUQ6AEIOjAD#v=onepage&q=algoa%2Bgearbox&f=false

Hope that helps

Dennis

[Brian WoodParticipant @brianwood45127]

Hello Ronald,

Your listing for the change wheel set up confuses me. If I understand it correctly, you are using a 45 mandrel driver, via a 40/21 coupled pair to either a 50 or 75 tooth wheel on the leadscrew, with an idler making up the distance.

What you don't say either is which setting(s) you have set the gearbox to. With that information as well it should be possible to see where you are going. If, as Neil has queried, you have a 3 mm pitch leadscrew on your lathe as well, then we will have to work out a new set of results for you.

Dennis has copied the link for the Machin [Hemingway kit] gearbox in my book on screwcutting gearboxes which I believe is a carbon copy internally of the original Algoa version and therefore matches the reduction ratios the gearbox gives.My book lists set ups for other screw pitches, such as BA, which I am pretty sure you won't find listed elsewhere

Regards Brian

Edited By Brian Wood on 06/11/2017 09:42:55

[KWILParticipant @kwil]

I am not aware that Myford ever fitted a Metric Leadscrew to the ML7. No reference is made to such an item in any Myford Literature that I have seen.

[Brian WoodParticipant @brianwood45127]

KWIL,

I agree with you that Myford did not offer a 3 mm leadscrew as a fitting on the ML7 but some individuals are capable of making and fitting their own; Marin Cleeve was a great experimenter for example

I believe Ronald is resident in the Netherlands so the possibility does exist and really, until we know all the parameters he has used in his set up, we are in the dark.

Regards Brian

[Clive Brown 1Participant @clivebrown1]

If the OP's figures are reasonably accurate, ie 1.8 instead of 2mm pitch, then a 3mm pitch leadscrew wouldn't explain a 10% error.

[Neil WyattModerator @neilwyatt]

Posted by KWIL on 06/11/2017 11:33:14:

I am not aware that Myford ever fitted a Metric Leadscrew to the ML7. No reference is made to such an item in any Myford Literature that I have seen.

I have heard of it being done, I think you might be able to use one intended for a Metric S7.

[Neil WyattModerator @neilwyatt]

Posted by Clive Brown 1 on 06/11/2017 13:23:12:

If the OP's figures are reasonably accurate, ie 1.8 instead of 2mm pitch, then a 3mm pitch leadscrew wouldn't explain a 10% error.

Yes, but he said 'more like' 1.8mm, which I assume meant he was estimating the pitch.

[Ronald HertogParticipant @ronaldhertog38923]

Hi All, Thanks a lot for all the quick responses,

I've measured the leadscrew, it has 8 threads per inch. So the standard leadscrew was used in combination with this gearbox.

The chart i have calls out for the selection fork set to 8 tpi in combination with the changewheels 45, paired 40/21 75, to form a 2mm thread pitch on the part. The 50 gear i described is indeed a idler.

However taking a closer look at the chart i believe there might be some mistakes in there.

According to the chart the changewheel setup can be used to produce the pitches wrote down below. the second number is the gearbox lever tpi position.

0,2 40

0,4 20

0,5 32

0.8 10

1.0 16

2.0 8

As you can see, there is a strange thing in there, choosing a 1.0mm pitch in this chart uses a 16tpi selection. when a 0.8mm pitch asks for a 10 tpi selection.

I estimated the wrong pitch on the part, i only own a standardized pitch gage with either 1,75 or 2mm pitch. the pitch it produced was short of 2mm and

[Ronald HertogParticipant @ronaldhertog38923]

@DMR, Checked out the book written by Brian Wood, funny to realize the writer of the book is actually giving me advice! I'm going to try those change wheel set up Brian describes in his book. Very handy!

[Brian WoodParticipant @brianwood45127]

Hello Ronald,

I've looked again at the tables in my book, they don't go below 0.5 mm metric pitch. By changing the leadscrew wheel to 75T, the mandrel wheel to 20T and setting the gearbox to 40 tpi you will get a pitch of 0.4 mm if that is useful to you.

It is pleasing to hear you are going to use the tables in the book.

And just out of curiosity with the set up you have described and going back to the chart you have just listed, working through the figures, I get the following values of pitch;

0.40; 0.80; 0.50; 1.60; 1.00; and 2.00 mm for the set ups you list You won't get down to 0.2 mm at all.

Regards Brian

[Brian WoodParticipant @brianwood45127]

Hello Ronald,

I've sent you a PM [personal message] Look in your Inbox to read it

Regards Brian

[HopperParticipant @hopper]

Posted by Ronald Hertog on 08/11/2017 19:28:26:

@DMR, Checked out the book written by Brian Wood, funny to realize the writer of the book is actually giving me advice! I'm going to try those change wheel set up Brian describes in his book. Very handy!

Support a starving artist: buy a hardcopy of his book. I just did after looking at the linked preview above. Looks like a good addition to the library.

[Brian WoodParticipant @brianwood45127]

Thank you Hopper, wonderful propaganda indeed!!

Brian

[HopperParticipant @hopper]

Posted by Brian Wood on 10/11/2017 13:44:56:

Thank you Hopper, wonderful propaganda indeed!!

Brian

You're welcome. I look forward to your book's arrival. It looked very interesting on the preview. Been thinking for years about making one of those gearboxes for the Mighty Drummond. Have thought about using minilathe gears to make it more compact. Long term project though…

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