Tufnol Tumbler Gear

My Myford Super 7 has Tufnol tumbler gears. I wasn’t really aware of this until a loud bang emanating from the gear train required investigation. I was trying to cut a 9 TPI Acme worm for my Divider project (MEW 295), and because I was waiting for a delivery of EN1A steel bar, was experimenting with a bit of stainless I had kicking around.

The Tufnol gear had lost three of its teeth. A quick search on the internet revealed some imports made from Tufnol rod and not recommended, or a supplier in the Netherlands who charged £20 for delivery.

Before I made a decision on parting with cash I decided to investigate why I’d had the problem. I read that the Tufnol gears are there to act as fuses that ‘blow’ under excessive loads. I checked out the lathe and everything was running fairly smoothly. I then read somewhere that making light cuts on stainless causes it to work harden. The tool I was using was a home made form tool, and I guess it grabbed and locked the lathe up, but I wasn’t sure.

I knew the next thing I did wouldn’t work but it cost nothing so I printed a 30 tooth gear on my 3D printer. This had the advantage at least of giving me a dry run on strip down and reassembly of the tumbler mechanism. The gear ran quite well until I put a light work load on it. I guess you shouldn’t use a 3 Amp fuse on a 40 Amp load.

The lathe was out of operation and I had a worm to make, but I couldn’t bring myself to send £50 plus to Norway. So I decided to buy some Tufnol and make my own gear. I spent £30 on a 300 mm square by 10 mm thick Tufnol Whale sheet from Direct Plastics. After a couple of attempts at making a decent fly-cutter, I managed to make a half decent 30 tooth gear which has now been in use for a couple of months. Did I make the right decision? Maybe not, I’ve just checked and the Myford site is now offering this item for £20. But should the fuse blow again I’ve enough Tufnol to make quite a few more.

Good job.

I'm not sure if Tufnol was used as a "fuse" or was it to reduce noise and wear on gears that run at or near full spindle speed almost constantly? The steel ones on my ML7 sure announce their presence, and its top speed is half that of a Super 7.

Frankly, I think well done. And even if it's relatively short lived, you have at least achieved something, and can do it again if necessary.

Peter G. Shaw

.

+1

To be honest ... I think the “fuse” story is a convenient myth, started by a supplier of dodgy components.

MichaelG.

The late great Sir J used to supply these to both Myford and on his own web site. NEVER use Tufnol bar stock for gears as first few rotations will strip all the teeth. Bar stock for bearings, sheet for gears. Noise reduction AND fuse.

Regards Ian.

The gears must be made from sheet tufnol with the gear axis square to the surface. This is because the grain, like in wood is on your side.

If anyone needs these Super 7 tufnol tumbler gears, and doesn’t want to make their own or pay through the nose, Steve Tracey has recently been offering them at £15 each or £25 per pair including postage. I bought a pair and the quality and fit are excellent. No connection except as a very satisfied customer. Steve can be contacted via email: [email protected].

As there is no shear pin in the Myford leadscrew drive train it would be unwise to replace the Tufnol with cast iron or steel. A broken metal tooth can take out a whole set of gears if it gets in the wrong place as the damage can be replicated on each gear. Leaving the banjo less than fully tightened is a ploy I have heard of to try and save the gear train but this must be hard to judge and an accidental disengagement will ruin the job. The Tufnol gears are an expensive shear pin substitute but if you don’t break them what other damage would be done in a crash? Screwcutting or feeding up to a shoulder only takes a moments loss of concentration to have a crash, I am luckily only on my second set of Tufnol gears but I have a set in reserve.

Mike

I concur regards the Tufnol gears. Steve also produces the excellent Meek/Myford carriage handwheel. Again no connection except as a very satisfied customer.

Certain pillar drills used to have Tufnol drive gear on the motor, as previously stated made from sheet material. Cant remember the spec but I do remember it had the number of laminations per inch. These were also large DP gears, like 4 or 6.

Of course you did the right thing. Making gears is fun.

This previous thread may be of interest: **LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=141344

MichaelG.

Um. . . Why don't you just order one from Myford.

**LINK**

regards Martin

Oh and incidentally in case you don't realise the front one is 28T and the rear 30T.

regards Martin

Edited By Martin Kyte on 13/07/2020 17:20:09

There are some out there in what appears to be genuine Myford packaging that appear to have been made from rod.


They don't last very long.

Have a look at the Myford Group on Groups.IO Adrian.

One of the guys on there recently made a batch of tufnol replacement gears in the two sizes - and they were very reasonably priced (even I purchased a set). Very nice chap to deal with too.

Regards,

IanT

Ian

The chap offering tumbler gears on Myford Groups was Steve Tracey.

I posted his prices and his contact details 9 messages back.

Mike

Which is why I suggested you get them from Myford. I'm amased at the number of people who troll around the world looking for Myford spares when you can get them from Myford's themselves. Yes I know it's not the original family, but the new owners did take over the buissness including spares supply. I could maybe understand if the item was very expensive, not sure I would be to quick to buy a new topslide for example without looking at options but £20 for a gear?, I wouldn't hesitate.

regards Martin

No connection just a happy customer

Note that though some talk of using sheet not rod, and "grain", there is Tufnol and Tufnol!

The name is the company, the product has assorted names but comes in two primary types to various recipes.

They are Synthetic Resin Bonded Paper, and ~ Fabric. You can generally tell them apart by sight.

Use the latter for gears; but do look at the manufacturers' published details to select the right one because that product variety is to cope with such a variety of applications. (The paper types for example are rather brittle, but ideal for electrical insulators.)

As an aside, cutting a thread close to the lead-screw's own pitch does put a heavy load on the machine, so you would need light cuts which as you suggest could have resulted in work-hardening on the stainless-steel, perhaps depending on the particular grade of steel.

In the previous thread, linked above, I stated I would change to aluminium if my already slightly damaged tumbler gear were to fail. I reckon it would be now a 3-D printed jobbie as all sorts of reinforced filament materials are now readily available and the printer is sitting waiting for a job such as that.