Lathe crash!

When the dial pinion wears out, some simply replace it with a plastic spur gear of the right size and tooth count - they do not usually do anything more than follow the lead screw and the plastic will soon conform to the shape of the thread.

No wear, it's what happens at the edges of a worm wheel. This is a detail of a home hobbed worm wheel for my traction engine steering:

If I hadn't truncated the ends of the teeth they'd be pointed, as per the photo posted by Chris.

Andrew

Having done the same thing, on power traverse, rather than screwcutting, a 5mm dia Rollpin is MUCH too strong!

"Shearpin" (Rollpin) did not fail, but it took some work to unjam everything, ready for repair. (Needed new pinion / shaft, and dressing of the rack)

After repairs, repaced the Rollpin with a 5mm brass shearpin, but came to the conclusion that that was still too strong, so removed it and drilled a 2.5mm down the centre before replacing it.

So far, no failures, (Has withstood 0.100" cuts in steel with feeds of upto 0.016"/rev) but if I do make another boo boo, the damage should be less.

Howard

Finished put everything together yesterday - looks like it's working fine. For a shear pin I'm using an aluminium pin for now as I don't have any brass available at the moment.

I know the frustration now Howard, luckily for me the WM280 comes with a clutch on the power feed shaft which saved me lots of times!

While at it I examined the change gears on the banjo to see if anything suffered as a result from the jam-up - and sure enough I found one of the keyed bushes cracked. Not sure if it's the result of what happened or it it was there before, but the material for the bushes is quite brittle. The question is can these be purchased? Machining one seems out of question. Really hate the change gears system on this lathe, if I could find a cheap source of gears I would do another banjo with a gear train set for regular machining.

A simple silver soldering job?

.

That would probably depend upon the nature of the unidentified 'quite brittle' material.

MichaelG.

I've wondered about replacing these, not because I've ever broken one, but because I often drop stuff on the floor and it disappears for 10 years.

If not available as a spare, NDIY may have meant silver solder as a way of making one from scratch:

1. Turn and bore the round part of the bush to size (easy)
2. Broach an outer groove. (bit fiddly, but can be done in a lathe)

Then make the rectangular key. Easy on a milling machine, a craftsman could file one by hand, and it could also be made by facing on the lathe. The main problem on the lathe is holding a small part.

Finish by silver soldering the key into the round part. (This might not be mechanically necessary but I would lose a loose key in seconds.)  Loctite might do.

Dave

Edited By SillyOldDuffer on 23/12/2018 10:37:34

Yep, he said making or purchasing, not repairing. silver soldered because the slot might not be deep enough, but, as you say, loctite might do.

No real problem to machine from solid if you have a rotary table.

No problem holding it to cut a groove if you cut teh groove while it is on the end of a big lump of bar, just start the parting cut to give the tool some runout space, plane the groove and then part off

What can't be seen in the photo is that there is not going to be much metal left when the slot is cut so in the event of a jam the solder may fail and you will split the round part from one of the internal corners down to the bore.

Should be an extra one in the toolbox anyway, there was with mine

I use aluminium modelling tube as shear pins, following my 'episode' of Saddle meets Headstock whilst under power.

So far so good as none have sheared.

Geoff - Fingers, toes et al crossed as I do not want to go through that again.

Thanks for the response, I dont have brazing equipment, but could try giving it a spot with the tig. I'll probably destroy it in the process as I don't know what the material is (could be cast iron?)

I have a spare one Jason, so for now I'm safe, but the whole set up is bugging me - the sleeve is a very tight fit, and I have to be extremely careful tapping it into the gears as the material has a tendency to crumble (if you see the end of the key in the photo you'll see what I mean). Also, the shafts on which the gears sit are not exactly the same length, so one is fine, the other is slightly shorter, so when I tighten it up the gear set will bind - fiddly to say the least!

So I'm thinking how I could make something simpler to live with. I a rotary table is on the top of my wish list but I don't have one yet so I'll either wait till I get one or thing of something else...

.

So it would appear, in retrospect.

MichaelG.

I usually set my long travel trip to just clear the chuck. Have to remember to reset it if working a bit close to the chuck, but the option was available on my hobby lathe from about sixty years ago.

So much for progress with modern lathes, if they don’t have these simple trips which have been available for decades!

The other problem you may find with soldering will be when you come to harden the fabricated part. Don't think I would want to leave them soft as they are spinning all the time at quite high speeds.

Let's see if this might work. If I had to eliminate the keyed bush completely and instead put a bronze bush on each gear. Then to stick a pair together I would use two dowel pins (push fit) I reasoned that two 3mm pins will have the same shear surface area as a 2x5mm key (that's what the keyed bush has) so they should in theory hold.

I tried some sketching - the largest and smallest gears I have is 80T and 20T

My 14DP 20 tooth gear was driven, or drove, by one pin of about that size. All the drive train gears were fitted with one pin - either 3/32nd or 1/8th. Little more space, but could be 3/16th, possibly - but there was not a lot of space between hole and root of teeth.

Or file the underside of the key to fit the circumference before silver soldering to avoid making those stress concentrating internal corners.

Neil

....................

Sintered bronze, by any chance?

If so - and I remember correctly - it can be cast/press-formed into shapes ...... and also has a shear strength of something approaching cast cheese.

Will

There's not much space to machine a slot for a key on the bush, Neil. The bush is 14mm od and 10mm id so with 2mm wall thickness to play with there's not much one can do...I think.

Will, it's silverish grey in colour so I'd think is something ferrous, will touch it with a grinder and see what spark (if any) it will give off, should give an indication.

I'm tempted by the pin approach, - just in case I come to need them, any one knows where I can get mod 1.5 gears at reasonable prices? Warco does not list them on their web shop but I'll ask.

Beltingonline are reasonable, I've used their gears a couple of times on engines.