Ideas to best hold blanks with out turning

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You DON'T NEED TO CUT THE BACKER! MAKE IT SLIGHTLY SMALLER THAN THE DEDENDUM RADIUS.

Look at Clipspring's video here. Actually he does slightly go into the backing but he could have used a slightly smaller disc and not cut into it. You can see that the tops of the teeth, which are weakest, and indeed most of the flanks, have no backing.

Really appreciate the advise so will make in future the backer smaller then I can use most things but Delrin seems a good idea. Will need something that wont bugger up the end mill aswell when making the spokes.

How would I cut wood if I went that way. i have a wood tool rest but is it viable to use wood in place of say delrin?

On second thoughts I could machine to a smaller diameter the aluminium backer to avoid the cutter hitting it and then the end mills should be fine milling the spokes out???

Chris

Edited By Chris TickTock on 18/03/2020 15:42:21

**GT insert or an HSS tool with plenty of top rake would be best for wood and used just like you were turning metal.

Endmill is just as likely to get tip build up as the gear cutter in aluminium without lubrication.

Edited By JasonB on 18/03/2020 15:44:38

Well I have learned something, it looks as is i can use the cutters I have to cut an odd small bit of wood to make a backer;

Hope link comes out as pasting it was a none runner but it links to a clip using a metal lathe to make a wooden item

https://www.youtube.com/watch?v=Cebi1IL9q9s

Chris

Or this one with carbide bit

https://www.youtube.com/watch?v=5GYyyF5YKIU

chris

Unlike metals, plastics and most other engineering materials, wood isn't equally strong in all directions. It's likely to split along the grain.

I'm not convinced providing a solid sacrificial back will stop burring especially if the back support is soft - like Aluminium, plastic or wood. I'd be inclined to only support the gearwheel near the edge, leaving the teeth to their own devices.

Note I've shown the arbour with a central gripping hole plus six holes on an PCD. The axle hole on some gears is too small to allow them to be bolted down firmly. Instead, the gear blank can be held by 3 or more nuts and bolts passed through the outer holes. They're arranged to pass through the gears quartering (which might be cut later). Use the most convenient method. It's not unusual to make arbours to suit the task - 3 holes 4 holes, axle only, whatever is needed to get the job done.

Cut teeth from front to back and de-burr the gear's back side by rubbing it on flat emery paper after the teeth have been cut.

It's often a good idea to experiment to find what works best for you and your equipment. Please report back!

Dave

When you reply to a post and click "quote", put your cursor right at the bottom of the window below the end of the vertical bar at the left before you start typing - then it will be quite clear what is your text and what you are replying to.

You have two things to do.

1. Cut the teeth, which needs the wheel blank on an arbor to fit the dividing head so the cutter can reach the periphery of the blank For this a nut and small washer on the outside, and a backing plate made of whatever you lies as long as it's reasonably rigid, is needed. If you like you can add a pin through the blank into the backing or use superglue, but if you do the nut up tight you shouldn't need anything else as long as you're cutting symmetrical teeth because the cutting force is along the wheel axis.
2. Cross out to create the spokes. The usual approach is to drill a small hole in the area of each space and use a piercing saw. Frankly I think it's fiddly and quite hard to do without practice. You just hold the wheel (after the teeth are cut) in your fingers and use a "vee" cut-out saw table to support it, the cutting action being on the downstroke so it pulls the blank onto the table. There's another Clickspring video showing this, though he has a power fretsaw and filer.
   
   For milling (very non traditional!) the blank needs to be stuck down to a table, e.g. a rotary table. This needs a separate backing. For this sort of job on my mill (admittedly using CNC) I stick the work down on a sacrificial plate with a small screw (M4?) through the centre hole, using superglue. The plate could be aluminium, or I tend to use Valchromat which is an engineered wood. Getting it off can be done by heating, e.g. putting the whole thing in a saucepan and boiling it. Or use blue masking tape on both surfaces with the superglue in between - doesn't hold so well but easier to part. Use a small mill, say 1 or 2 mm for a wheel the size you're making. Make the max DOC only just enough to get through the material - if you're backing with ali there'll then be the minimum amount of ali swarf to gum up the cutter and anyway only on the last cut.

Thanks Jason for the help with the Quote as well, will try to remember that.

Agree with a lot of what you say but will as always note all and try various ways.

Chris

john sorry I meant thanks John

chris

update:

Whilst waiting for my delrin 9plastic0 to arrive I got bored and tried making the backer from wood.

Results ply not easily machined as breaks off but mdf worked a treat. If only used in small amounts I think acceptable (dust). chris

I agree with Tick TOCK. When it comes to asking stupid questions, I am in the Top Ten. I do it all the time, why ? simply because I don't know the answer, therefore I don't regard it as stupid. Maybe others do, but most Members don't and are only too happy to enlighten me. Don't be afraid to ask, it,s the only to find out.

I don't make clocks so I cannot help in this case but I still learn something from such Posts.

Appreciated Larry..well put

chris

Amazing some of the stuff on this site!.......personally, I use hardboard for backing wheel blanks and always cut at least two together then select the best looking one....

Remember the old comment that there are no stupid questions, only stupid answers.

Thanks Bob, Hardboard comes in the right sort of thickness and is cheap enough so will grab a bit next time I dare enter B&Q.

Chris

I'm not a clock-maker but treating this purely as metal-working, would it be worth making the washer - which can be of almost any reasonably rigid plastic or metal - to dedendum diameter as John Haine suggests, but dishing it slightly so the pressure is applied close to the cut?

Thanks Nigel, an interesting and worthy idea

Chris