Banjo cam won't tighten

[scooby]

I noticed today the cam on my lathe won't tighten. Well, it does tighten but it works its way loose instantly.

I thought it might be a case of just adjusting the cam bolt, but that just changes the position (on an imaginary clock face) of the lever when the cam is fully tightened. It springs loose regardless.

A few observations:
1. with the banjo removed, the lever/cam will rotate fully but seems to bind (presumably on the collar on the banjo) but I cant see where.
2. With the banjo left in the same distance from the headstock but at different extensions from the bed, the lever movement distance changes and in some places the springing loose ceases.
3. Inspecting the banjo cam, there is a section of the bar that has the black coating worn away.

So I'm assuming its this worn section or the cam bar could be bent..that is causing the problem?

I'm note sure if it is bent, it 'looks' ok. I've never gone mad tightening it so I'm a bit surprised.
Any advice appreciated.

 

[MARK.B.]

What lathe do you have scoobya pic or two may help give someone more detail to help answer your problem

 

[scooby]

Oops..bit stupid not mentioning the lathe model Its a KS Midi 350, its the same as the Axminster Trade 350 (AT 350?).
https://hopewoodturning.co.uk/lathe...350/114/ks-midi-fu-350-woodturning-lathe?c=34
I'll get some photos tomorrow, I'm just off out for a bike ride.

 

[Sachakins]

It could be that you need to slacken the slide nut off a bit. Had similar on my coronet after servicing it. If the slide plate is to close to bed, then you can't get the Cam rotation sufficient, and it will back off. I backed off my nut by half a turn and the Cam Lock works fine now.

 

[scooby]

It could be that you need to slacken the slide nut off a bit. Had similar on my coronet after servicing it. If the slide plate is to close to bed, then you can't get the Cam rotation sufficient, and it will back off. I backed off my nut by half a turn and the Cam Lock works fine now.

Thanks mate. I did have a go adjusting the bolt yesterday but the cam kept springing loose. Admittedly, I was cold and hungry so it was a half arsed attempt at sorting it. I'll have a proper go later.

 

[Bob Chapman]

I once had an identical problem on my Vicmarc. The problem was dust collecting on the cam lock. Tightening the cam simply compressed the dust and didn't hold for long. A good clean improved the grip immediately. Strangely, it never happened again.

 

[Paul Hannaby]

A agree with Bob, problems with cam locks are often solved by a combination of a strip down and clean followed by reassembly and adjustment if necessary.

 

[Richard_C]

I had a similar issue with my Record DM305 - similar bed.

As above, good clean including under the bed where the cam lock washer slides. Rub of beeswax stick on the bed so it all moves nicely. Counter-intuitive I know but a wipe over of the cam and the bits of casting it contacts with light oil (3 in 1 type) - that means the 'ooomph' you put into tightening all does that rather than be disspated on sticking threads etc.

Then a patient adjustment of the nut so that the cam tightens at just about 90 degrees from vertical - too tight or too loose are equally problematic.

Not had any issues since.

What's the black coating? Mine is shiny metal so nothing to wear off, I wonder if some cosmetic finish is more nuisance than use?

 

[Adam Pinson]

I have this issue too on my RP DVR-xp.... it gets loose but even if i slightly overtighten the hex bolt it binds.... a real pain as i have to keep stopping to adjust

 

[scooby]

Thanks for the replies everyone.
The black coating isn't a paint coat or anything like that. I'm not a metal or paint expert, its probably just the surface of the metal but there is a patch that is shiny/silver colour. I cleaned it with some degreaser and it made the rag go black but there was no visible difference to the bar. For any versachuck owners, it looks like the same metal as the chuck key.

I found out what the binding was. The circlip on the front of the banjo cam (near the lever) catches on the recess of the banjo casting in a certain position. So not a big issue.

I couldn't see any dust in the cam but I gave everything a good clean and its gripping like it should now.
Thanks for all the help

 

[Richard_C]

I have this issue too on my RP DVR-xp.... it gets loose but even if i slightly overtighten the hex bolt it binds.... a real pain as i have to keep stopping to adjust

RP DL305 similar bed. I reckoned that when you moved the banjo along the big "washer" under the slot didn't quite keep up so when you tightened it it was a degree or few off level. Seems tight, get a bit of sideways pressure or vibration and it loosened.

Answer was always make sure cam is at its loosest when moving, easy for the handle to drop off vertical and pull it up a bit, and when you arrive jiggle the washer ro make sure it is properly flat before you tighten.

The bottom of the casting had a few rough bits as well althought it is machined where the washer runs. Cleaning that up and beeswax under as well as on top helped a bit.

A better design might be to have a rectangular plate moving under the bed rather than a round grooved thick washer.

 

[Adam Pinson]

RP DL305 similar bed. I reckoned that when you moved the banjo along the big "washer" under the slot didn't quite keep up so when you tightened it it was a degree or few off level. Seems tight, get a bit of sideways pressure or vibration and it loosened.

Answer was always make sure cam is at its loosest when moving, easy for the handle to drop off vertical and pull it up a bit, and when you arrive jiggle the washer ro make sure it is properly flat before you tighten.

The bottom of the casting had a few rough bits as well althought it is machined where the washer runs. Cleaning that up and beeswax under as well as on top helped a bit.

A better design might be to have a rectangular plate moving under the bed rather than a round grooved thick washer.

The plate under mine is rectangular but i am going to tear it all down and give it all a spring clean, maybe that'll do the trick, cheers