Gear blanks - which materials, or where to buy?

I would like to have a crack at making a 3 jaw chuck, and am looking at the scroll / bevel gear component. I know they are usually all one piece making it very complex to make, so I am starting simple and just trying to figure it out step by step.

If I wanted to make a bevel gear, what would be the stock material of choice, or are there dedicated gear blanks or castings you would need to buy? Ideally it would have the extra material on the reverse side for the scroll, and then I will probably need to find a CNC machine for the next step!

Cheers

Ross

You could just buy spare scrolls which have the bevel gear cut on them and three pinions, probably cost you more than a hobby chuck though.

A quick look at the materials used by gear manufacturers comes up with,

HPC bevel gears are supplied in EN8 and Davall in either EN1A or EN32,

these are their standard materials, I don't know if the ones used in chucks would be made in anything different.

John

You would want to make the scroll plate, with bevel ring gear on the back of it out of steel. Ideally a tough steel such as 4140, which would make it tough to machine also. Cast iron would be a bit brittle on those small bevel teeth.

Or you could look into the alternative type of three-jaw chuck that does not use the three bevel pinions and the main bevel ring gear. The whole body turns instead, using a lever in a hole in the body and one in the back plate. I forget what this type of chuck is called. But a bit of googling around might find one. They are usually small chucks, 50 or 65mm diameter but could be made bigger.

ISTR the Model Engineers Workshop 25 year special edition had drawings in it for making your own four-jaw chuck, which is a lot more do-able than a three jaw as you only have to screwcut a square thread for each barrel, instead of a bevel gear, then screw cut the chuck body to match. If it were me, that is the way I would go.

None of them would rate as a beginner's project or even close to it, IMHO.

Edited By Hopper on 25/06/2018 07:20:13

PS, lever scroll chuck is the name I was trying to think of.

I thought the bevel gear and scroll were normally on the same side? Otherwise the chuck body would need to be quite thick.

I would think that a medium carbon steel would be fine. I've made bevel gears in cast iron, bronze and aluminium, so steel would be no problem. To make a proper bevel gear you'll need a CNC mill and some CAD/CAM skills. However, in this low speed, low accuracy application the approximations for use on manual mills will be fine. While a CNC mill would be helpful for making the scroll it could be done with a universal dividing head and a vertical mill. The dividing head would need to be vertical and geared to the table so that as you turn the dividing head the table also moves the cutter away from the centre of the plate.

While not stricly necessary it would be helpful if the number of teeth on the bevel gear is a multiple of three.

Andrew

Not on chucks that I have worked on. Commonly the scroll side is flat and the other side has the bevel gear on it. The whole thing is usually pretty thin due to the very shallow angle of the bevel gear.

Edited By Hopper on 25/06/2018 10:49:54

Surely the overall depth of the chuck body will be far more affected by the diameter of the mating pinion rather than the pitch angle of the bevel gear?

Andrew

Hi, thanks all for the replies. I am really wondering what kind of stock to buy. For example if I wanted to make a 4 inch bevel, I am guessing I would need a piece of solid 4 inch diameter stock, but most of the suppliers online seem to top out at 2". Would you usually buy a specific gear blank, and who would you get such a thing from? Google finds me lots of people that want to sell or make me gears, but not blanks unfortunately : )

Also is unlikely I will use the chuck, I want to make it "just cos"

The greater the angle of the bevel, the larger the diameter of the large end of the pinion. So bit of both I suppose. The type of chuck I am familiar with and referring to is like this:

The angle of the bevel is very shallow. Maybe 10 or 20 degrees or something like that.

A good steel supplier should be able to cut you a slice of 4" diameter steel bar. Try College Engineering Supplies. Others I am sure can suggest local possibilities. If worst comes to worst, get a piece of plate cut in a circle by a laser or waterjet or plasma cutting outfit.

No such thing really as a standard gear blank you buy off the peg. It's just a round piece of metal.

You could possibly cut (or mill) the scroll in a standard lathe with a custom made gear drive and linkage from the change gears to the cross slide leadscrew.

ISTR reading an article years ago in MEW or ME on cutting the sections of scroll thread on the jaws that meshes with the scroll. The radius on each side of each tooth is different. The trick is the teeth have to mesh with the scroll plate where the curve is large near the outside diameter, but also mesh with the scroll plate groove where it is a much smaller radius in toward the centre.

Edited By Hopper on 25/06/2018 12:08:13

Thanks Hopper, I have emailed CES to see what they say. I couldnt see 4" bar on the site, biggest was about 3 and a half. I think I will need about 4.5 inches anyway for all the cock ups

Cheers

Ross

Oooopsie, dunno why I thought that the scroll and bevel gear were on the same side.

The pitch cone angles are determined by the tangent of the ratio of the number of teeth on the pinion and the gear. But the pitch circle diameter at the outer edge of the pinion is set only by the number of teeth and the diametric pitch of the pinion. It is not affected by the pitch cone angle.

Andrew