Modifying my lathe

[p0689109]

I bought a lathe a few years ago and its driven by a electric motor (what else) which is then connected to an old car gearbox to allow speed changes. Now the connection between the two was, wait for it, a bit of rubber pipe and two jubilee clips. It might have worked when the chap who owned it fitted it and the rubber was new but it has past its best now. Also the setup he had meant that the motor was not really squared up to the box and the give in the rubber gave that join the flexibility it needed to drive the lathe. So I have decided to join the two with a more direct drive. I have already modified the whole rig and the new motor I bought when I got it id directly lined up and at the same height of the gearbox input shaft. The motors shaft is 19mm in dia and the gearbox is 22.5mm dia, I have a piece of thickwalled pipe that as near as dammit fits the gearbox shaft(its the clutch end and so has flutes/splines) and in this shaft there are holes which do not go all the way through. My plan was to drill one of them all the way through the shaft so that I can pin it to pipe. The motor end will need a bush and also will need its shaft drilling. My question is I assume these shafts are hardened and my cobalt drills are not touching it. The original hole is a smidgeon over 2.5mm and so I used that size drill to drill through to the other side at a low speed. So what drills will do it? I have read that masonary drills work but on the motors shaft how do I get it to start?

 

[Gritineye]

That rubber hose and jubilee clip connector was a common way of doing it years ago, used on a lot of engines, dynamos and such. Although it looks a bodge it has advantages over a solid coupling.

 

[p0689109]

Yes but the couple of little jobs I have used it for it slips after a couple of mins and after tightening it its the same.

 

[Gritineye]

Masonry drill will work if you grind it to have a keener edge, nothing fancy just angled back from the cutting edge for relief.

Try sticking some masking tape on the shaft it often works to hold position to get started, masonary drills seem to flex more the other types and may wander off on the way through .

I drilled a hardened tool holder that way yesterday.

 

[rikrobson]

Is the shaft not keyed?

 

[Bill Edwards]

Better cobalt drills. Some are great, some aren't - I have a set of Milwaukee ones which I expected to be good. They are, for mild steel... Anything hardened and they're not interested. Another set (8% cobalt rather than 5% which is probably significant) do drill through hardened metal as though it's mild steel.

I would actually be tempted to try a fresh piece of rubber pipe with two good quality (i.e where you tighten them with a spanner/socket rather than strip them with a screwdriver) hose clamps (try Hi-grip brand) which should get them nice and tight. It'll give a bit of room for misalignment and reduce vibration. Not wishing to doubt the accuracy of your alignment but unless you've gone to great lengths to machine everything to precision it'd probably benefit from some form of coupling which isn't rigid. If you do continue with your current method make it a sloppy fit so it has room to rattle/move.

 

[james butler]

why not go to a scrap yard and have a look round for a knackered clutch that will fit the splined bit and modify that to fit to the moter and then slip it onto the input shaft of the gearbox as was origenally intended

 

[Woody.v8]

You need something like this

or a fenner type couple like a cush drive setup on a motorbike.

 

[penfold]

I'd be surprised if a gearbox input shaft was hardened to the extent it can't be drilled with ordinary HSS drills; when drilling it, grind or file yourself a flat and put a big fat dink in it with a nice sharp centre punch, then it should drill even if hardened. Alternatively just weld the tube to the shaft. As pointed out by the others unless your alignment is spot on you may be creating problems.

Consider making your own diaphragm coupling; make two matching bits of flat bar 2-3" long with holes drilled at either end, take the tube you have that fits the gearbox and weld a flat bar across the end(make sure its centralised and reasonably square), drill a hole near the other end of the tube and weld on a nut so a bolt or grub screw can clamp the shaft. Do the same with a bit of tube that fits the motor. Cut a disc of heavy reinforced rubber or a flexible plastic(old cutting board is good and can be got free) with a diameter equal to the length of the flat bars and punch/bore/drill/whatever 4 holes at a PCD to match the holes in the flat bars. Bolt it all up with penny washers and bob's your uncle. You may need to grind flats on the shafts for the clamp screws if you don't have grub screws with hardened points.

 

[zx9]

Consider making your own diaphragm coupling; make two matching bits of flat bar 2-3" long with holes drilled at either end, take the tube you have that fits the gearbox and weld a flat bar across the end(make sure its centralised and reasonably square), drill a hole near the other end of the tube and weld on a nut so a bolt or grub screw can clamp the shaft. Do the same with a bit of tube that fits the motor. Cut a disc of heavy reinforced rubber or a flexible plastic(old cutting board is good and can be got free) with a diameter equal to the length of the flat bars and punch/bore/drill/whatever 4 holes at a PCD to match the holes in the flat bars. Bolt it all up with penny washers and bob's your uncle. You may need to grind flats on the shafts for the clamp screws if you don't have grub screws with hardened points.

Sounds like you are describing the lower steering column links from an old Range Rover or Disco, would that sort of thing be a ready made option?

 

[Johnnybravo]

Google love joy coupling. Basically two bits of steel driving through a rubber/plastic cross. Allows for a bit of misalignment and cheap as chips.

 

[Rig Pig]

What about just converting to belt drive with a counter shaft to allow speed change? Smoothe drive with no complex alignments.
What size lathe are we talking about?
If you want I can take pics and dimensions from my lathe - 4 1/2" S&B with 1/2hp motor

 

[Triumphman]

Would this sort of joint work in a sliding application? Where two shafts meet, but might slide apart or together?

 

[Johnnybravo]

Got a nice 1/2hp motor, inverter and variable speed gearbox in the classifieds !

 

[p0689109]

Bill Edwards- I use Irwin drills
Woody v8 -I like those couplings, what are they called- I cannot read the names marked on the photos?
RK Robson -the motor has a keyway but no key at the moment
James Butler- Fondly enough that was my first thought but being such an old gearbox the input shaft has only 6 "splines" more like flat keyways really, and I doubt it would be realistic to try and find one at a scrapyard anyway
Johnnybravo- thanks for name of coupling I will look at it- next job infact! They look expensive mind!!
Thanks all for your thoughts.

 

[p0689109]

I forgot to mention that the motor shaft dia is 19mm and the gearbox shaft splines at the peak are 22.5mm or there abouts. So would those couplings cater for that Woody.V8

 

[Ton-up]

Google spider couplings.

 

[p0689109]

Thanks for your input gents. Having looked at all of them I think the lovejoy jaw coupling is the item I prefer. I have enclosed a few photos of the lathe. The first one shows the alignment as the centre pin is a drill shank I put in to make sure the shafts met in the centre.

 

[dannyp]

double or multispiral hydralic hose will make a coupling that can take a supriseing amount of power.

a personal favoret atm is put a sprocket with same number of teth and pitch on each shaft and then wrap some duplex chan around them

 

[p0689109]

I have spoken to the firm that supplies the lovejoy jaw couplings and they can supply one machined to match the gearbox spline at one end and to take the keyway at the other end for £53 pounds plus postage. They want £16 for that but I can organise my own courier.
Better photo of the alignment of the two parts.