Mini Lathe leadscrew key size?

This topic has 11 replies, 8 voices, and was last updated 26 February 2021 at 20:03 by not done it yet.

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18 February 2021 at 16:56 #528317
Carl Walker
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@carlwalker
Hi All,

Whilst changing the change gears on my Mini Lathe (A Warco Mini Lathe) I lost the small key that fits the change wheel on the end of the lead screw. Does anyone know offhand what size this is, so I can order some key steel stock of the right size? A quick examination makes me think it is 4mm x 3.5, or possibly 3.4, so I'd need to order some 4mm square I think, is this right? I'd rather buy some key steel instead of ordering the made key as a spare from Warco(if they even have it!) as I'm still building my stock of offcuts, etc

Cheers

Ricky Walker
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18 February 2021 at 16:56 #20162
Carl Walker
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@carlwalker
I need to know the size of the key that goes in the change gear at the end of the leadscrew
18 February 2021 at 17:17 #528329
old mart
Participant
@oldmart
I bought two boxes of mixed woodruff keys, one imperial and one metric on ebay. They weren't expensive and have saved time.
18 February 2021 at 17:58 #528337
Brian Wood
Participant
@brianwood45127
Hello Ricky,

I don't have a mini lathe but the keys are usually square section, I don't think Far Eastern imports use Woodruff semi circular keys. They are easy enough to measure as is the keyway they fit using a pair of callipers across the gap

Regards Brian.
19 February 2021 at 00:21 #528411
Carl Walker
Participant
@carlwalker
Hi Brian,

I did think it rather odd, but I milled and filed a small bit of mild steel down til it fit the keyway on the shaft, and it was 4mm wide. When I fitted one of the change gears, the key slot appeared wider than it was tall, and a quick measurement with digital calipers gave me 3.5mm high. This did surprise me a bit, as I was expecting it to be 4mm, although measuring the height of the key slot accurately was a bit difficult with the digital calipers, so that may account for it. It does look physically wider than it looks tall, though.

The bit of mild steel I cut down to 4mm is still 6mm on the other dimension, and I am having difficulty on figuring out how to hold it in the vice to be able to mill it down to size on the other dimension, so I'll have to think about it for a bit before I continue – I may end up having to make a special jig to hold it for machining! Just realised, I may be able to clamp it directly to the milling table, as the piece is longer than I need for the key, so I could clamp it at either end and mill to 4mm high in the middle.

And as you say, it is a straight key, not a woodruff key, sorry, old mart

Thanks

Ricky
19 February 2021 at 04:05 #528417
Howard Lewis
Participant
@howardlewis46836
Depending upon the manufacturer of the mini lathe the key for the change gears will be a polain key, either 3 or 4 mm wide.

Sieg made lathes use 3 mm but Real Bull (Who supply WARCO, I think ) use 4 mm.

Not sure about Weiss made machines., would need to measure the keyway in the Leadscrew

Howard

Edited By Howard Lewis on 19/02/2021 04:06:21
19 February 2021 at 09:48 #528440
Brian Wood
Participant
@brianwood45127
Hello Ricky,

The fit of a key in the shaft is deeper than in the pulley, for example a 4 mm key will be nearer 2.5 mm deep into the shaft and there will be some 'daylight' over the key when it engages the pulley. There are data tables published of the actual values for both metric and imperial sized keys.

Regards Brian
19 February 2021 at 10:13 #528448
not done it yet
Participant
@notdoneityet
4mm small? I need a key for a 3/8” shaft. It is 3/32” wide, at a guess. Might even be a square section.

I think I’ll take the easy route and mill a piece of steel thin at one end then finish it on the surface grinder.🙂
19 February 2021 at 10:19 #528453
Nick Wheeler
Participant
@nickwheeler
By the time you've figured out how to clamp it to the mill, you could have filed it to size and fitted it.
26 February 2021 at 19:00 #530388
Nigel Graham 2
Participant
@nigelgraham2
If making a key from stock, cut its width and height on the end of a piece of stock bar then saw and file to length. You may need put a stop behind it to keep it rigid, or machine it sandwiched between sacrificial pads.

The critical dimension is width. You could thin the end of a piece of plate to that, hold it vertically to cut it across by slitting-saw to height, then hand-saw to length and clean up by file.
26 February 2021 at 19:05 #530390
Oldiron
Participant
@oldiron
Posted by not done it yet on 19/02/2021 10:13:12:

4mm small? I need a key for a 3/8” shaft. It is 3/32” wide, at a guess. Might even be a square section.

I think I’ll take the easy route and mill a piece of steel thin at one end then finish it on the surface grinder.🙂
26 February 2021 at 20:03 #530407
not done it yet
Participant
@notdoneityet
Yep, milled the end of a piece of virtual scrap, then ground it to size on three sides. The last side was filed. I figured that if my first effort was NBG, there would be spare metal to go at. As it happened the first filing was successful and the new fiddly little key fitted well.

It was some more good practise with the SG as well. I’m not good enough to file all four sides as accurately as the way I did it – it would probably have needed more than one attempt and still would not have fitted as well. The belt sander would likely have been an alternative to get ig to size – if the SG was not there.

Edited By not done it yet on 26/02/2021 20:03:57
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