Turn Of The Screw

Hello Everyone

I wonder if someone could advise me on the simplest way to cut an oil/grease scroll.

I'm making some bronze king pin bushes. I want to carve a helical scroll through them to facilitate the distribution of lubricant. The bush itself will be about 20mm long with an I/D of around 13mm and a wall thickness of approximately 3mm.

I'm thinking of putting the bush in the lathe chuck, putting a sharp boring tool in the tool post, turning the chuck by hand and advancing the tool with about 1mm depth of cut. I'd like to do it in one pass.

Do we think that will work?

Thanks, as always in advance.

Best Martyn

You can have a go but trying to cut a helical scroll on a lathe is not the easiest as the larger lead you generate [i.e.. your scroll vs a screw thread] the mechanical set up means you need the saddle movement to turn the chuck? Others will come along with more details I'm sure, also rough the bore do your groove & finish the bore as the last operation.

Tony

I agree with Tony as regards the boring after cutting the groove. However, I don't think you will be successful making the cut in one pass at 1 mm depth. I would be more inclined to put a circular, semi-circular section groove in at the greasing point. Grease will flow around the pin and eventually out the ends of the bush taking debris with it. A helical groove gives a direct exit to the outside, unless it is a figure of 8 pattern and kept within the ends of the bush.

Regards

Gray,

Hi Martyn

I did something similar for a Bultaco gearbox bush and as Tony suggests I had to drive the lead screw because using a mandrel handle in the spindle didn't feel right, something was going to strip. My lathe is the ubiquitous Chinese mini lathe with plastic change gears.

HTH

Cheers Michael

Dead simple use an internal grooving tool put on a cut of approx 10 to 12 thou and from the chuck end of the bush draw the tool thru the bush smartly as the lathe is turning, job done . Done it dozens of times, don’t make it complicated.

If you wanted to make it complicated you could watch this:

https://www.youtube.com/watch?v=TJH2q5ylJXM

Graham Meek has it ! Easy to do and will work well ! Noel.

Producing a shallow thread with a 10 mm pitch will be difficult.

I would prefer Graham Meek's suggestion of turning a plain groove on the line of the grease inlet, and relying on the clearance to distribute the grease.

To my mind this will have advantages

The entire bush / kingpin interface will be lubricated.

The grease will fill any clearance and improve alignment/fit..

Having grease oozing from the ends of the bush should reduce the risk of water ingress.

Howard

Hi Martyn,

If you have an engraving tool (graver or burin) use that to create a groove away from the entry point or groove as per Grahams post. In king pins this groove did not go all the way to the end of the bush.

Regards,

Nimble Neil

Set up to screwcut a coarse pitch and drive the leadscrew. Constant result and if you need to make th ecut in more than one pass each will follow the same path.

Thank you everybody.

I really like Noel's special tool, but it would be a bit of an extravagance for two bushes!

I think, in this instance, Graham's idea of the radial groove at the grease entry point has to be the way to go.

Again, very many thanks.

Best, Martyn from a grey and chilly Paris.