Lorch 6mm lathe

Snapper

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I wonder if one of you fine folk could do me a favour please. The photograph is of my recently acquired lathe in its rather rough state. The restoration is coming along fine but you will see from the illustration that in the dim, distant past the collet tightening knob (is there a specific term for this?) has been replaced with a home-made lever (arrowed) which could prove "interesting" when turning at high speed!

I intend to turn a replacement knob out of Delrin, but before I order the stock could anyone give me the diameter of the original knob?

Many thanks in advance.

untitled (1 of 1).jpg
 

gmorse

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Hi Snapper,

...but before I order the stock could anyone give me the diameter of the original knob?
They're in the region of 35mm in diameter, (my 6mm lathe has one this size at any rate). A smaller one would tend to prevent over-tightening!

Regards,

Graham
 

trim

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My 6mm Lorch with original drawbar knob is 32mm. My 8mm Lorch with original drawbar knob is 35mm.

This corresponds to Graham's comment about tightening.
 

wefalck

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The original drawbar-knobs were made from polished black Bakelite and had around 32 mm diameter indeed. I have made replacement knobs from black POM/Delrin, as black round Bakelite stock is virtually unavailable and flat stock is usually brown and also difficult to get in suitable thicknesses. While Delrin obviously is much less brittle than Bakelite (the reason for the absence of your knob), it is also a lot softer. This means it is more difficult to provide enough key to lock the knob onto the drawbar. The drawbar should be riffled at the end and the bore in the knob needs to be undersized by a good degree and pressed onto the drawbar. However, I am a bit concerned that this makeshift device on your drawbar may have eaten away the serrations. You can try to reconstitute to some degree the serrations with a graver or a fine three-sided needle file.

I gather the issue with the serrations and the lack of availability of suitable materials is why people tend to replace the knobs in brass (I have done so in the past too).

Here a new drawbar including knob that I made a short while ago:

MF-110.jpg
 

trim

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You can buy black Bakelite in flat sheet 8mm etc thick off ebay. Not sure how easy it is to get thicker though. The WW lathes I measured are 9.5mm thick, I can't measure the Lorch atm. If you are willing to cut it from flat, a hole saw works fine to make the required blanks.
 
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Snapper

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Great information here, thanks to all. Yes the serrations on my drawbar have been considerably flattened by the clamp device fitted by a previous owner. I was going to re-cut them with a file as suggested and also use an industrial adhesive. Whether this would work is open to guess as I am aware that Delrin is difficult to bond. Maybe Loctite may work?
 

gmorse

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Hi Snapper,

I was going to re-cut them with a file as suggested and also use an industrial adhesive.
I had to re-fit the original Bakelite knob, which was very loose, on my 6mm when I acquired it some years ago. I cleaned everything up, fitted three tapered steel wedges to centre the shaft and then filled the gap with Araldite epoxy resin. It's still absolutely solid and it gets used most days.

Regards,

Graham
 

Dr. Jon

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I strongly recommend against Delrin. It cold flows and will not hold up.

I like the idea of using epoxy to reproduce the serrations but I suggest you apply a mold release to the drawbar. That way you will be able to remove the grip once the epoxy has set up without damaging the tooth form. These handles wear or get chipped and it is useful to be able to replace them without having to cut them off.

I think the holesaw idea is brilliant!. However, bakelite will wear the teeth.
 

karlmansson

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I used to rebuild old, broken crystal reciever headphones. Fit them with new speakers (that weren't 2000 ohms in impedance) and rewired them making them useable with modern sound sources. Part of that was machining the bakelite ear pieces. It wore down the graver I was using like nobodys business. What is the proper way to machine bakelite?
 

Dr. Jon

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I have not tried it but I suggest carbide tools. That is what they use to drill printed circuit boards. Bakelite usually has a cotton cloth embedded in it which as silica particles which are very abrasive.
 
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Snapper

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I strongly recommend against Delrin. It cold flows and will not hold up.
Thanks for the observation Dr Jon. I have little or no experience of plastics so in one sense this material was selected more for its toughness than anything else. As I had already acquired it I have made the new knob and merely press fitted it to the drawer bar. It is a very tight fit and I cannot turn the knob in relation to the drawer bar whilst clamping the bar in the vice soft jaws. I will see how this goes. If there is a problem later, well I'll have to make another from an alternative material.

This is a shot of the fitted knob.

2-2.jpg
 

trim

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I have not tried it but I suggest carbide tools. That is what they use to drill printed circuit boards. Bakelite usually has a cotton cloth embedded in it which as silica particles which are very abrasive.
I have used the carbide insert tooling designed for aluminium, with the ground carbide edge rather than moulded. I assumed it would leave a better finish, and it worked nicely for me. I did not comparison test against the standard moulded edge inserts however.
 

wefalck

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I have not tried it but I suggest carbide tools. That is what they use to drill printed circuit boards. Bakelite usually has a cotton cloth embedded in it which as silica particles which are very abrasive.
Well, actually Bakelite proper does not have any cloth embedded, but is made from paper soaked in phenolic resin and cured between two heated steel plates. There is another, similar, material also based on phenolic resin and cotton. In Germany it is known under the trade-name NOVOTEX, in other countries as TUFNOL, and used to make, for instance, spur gears that run quietly. I doubt that such material contains silica. However, you never knows what Asian manufacturers use these days.

On the other hand, recently I bought some 'Bakelite' rods from an Indian source through ebay that turned out to be a NOVOTEX-like material, reinforced with cotton. It machined very nicely without wear on the tools and could also be polished:

ThirdHand-TufnolJaws.jpg
The jaws on this shop-made 'third hand' are made from this cotton-reinforced phenolic resin.
 

Snapper

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My lathe is finally up and running barring a few mostly cosmetic adjustments. Given the state in which I acquired it, the restoration has gone very well. My fears for the headstock bearings (the shaft would barely turn) was unfounded and there is no detectable play. The seized clamp screws succumbed to liberal doses of penetrating fluid and all corrosion was removed by hand and the surfaces gently polished and even the horribly grotty belts cleaned up very well with IPA.

Following advice from members of this forum, I acquired a 120w sewing machine motor and foot control which works very well indeed with easy speed control and sufficient torque. The before and after shots are below.

untitled (1 of 1).jpg Lathe restored.jpg
 
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Uhralt

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I'm surprised that a 120 V motor works in the UK. Do you use a transformer to bring the voltage down from your 240 V?

Uhralt