Hello Larry,

Cut in one pass, nibbling at it blunts the cutters.

Revs perhaps 100 rpm or of that order. Dry cutting if cast iron or brass, coolant for steel

Auto feed if you have it is best but be guided by how the machine sounds. If laboured then halve it.

Be sure you cut to avoid any chance of climb milling. Try to imagine what might happen if the cutter were trying to pull the job down into itself; that way lies disaster so cut the other way and it will be trying to push the job away from the cutter. The chips should be coming up to the surface from the tooth root.

Keep all other motions locked, just use the one that moves the cutter through the work

Good luck with it

Brian

It might be a good idea to practice on a piece of tidy scrap (but the same as the real job) material first?

Best regards,

Swarf, Mostly!

Larry,

Good point by Swarf, it will give you a chance to check through the whole thing and ensure your indexing is also correct without wrecking something important

Another dodge you might find helpful is when you are moving the fingers before cutting the next tooth. Put a cocktail stick into a hole behind the finger that is remote from the indexing peg, it makes recovery from accidentally moving the fingers when you move the peg round so much easier as it preserves a reference at each stage

And finally, remember to lock the main shaft through the dividing head before cutting each tooth so that the work is rigid when the cutter goes through it

Regards

Brian

Brian above mentions marking where the fingers were to enable recovery if you slip with the fingers on the dividing wheel. A variation on that idea that I have used is to mark the dividing wheel with a felt tip pin at each hole that will be used. The marks come off OK afterwards with most common workshop solvents. How workable the felt tip pen trick is depends on which holes you will be using and how close they are together. It does pay to go right around first with no power on and just making a little scratch on the blank at each cut position so that you can check that the division is correct.

Of course not all rotary tables come with dividing wheels, it is possible that you may be just using the scale around the edge and on the hand wheel. This is workable but takes extra care with the setting each time.

Generally I find that making blanks and setting up takes all the time, the actual gear cutting seems to go quite quick.

John

If you're using a regular pattern of holes you can cover the plate with masking tape and mark each hole you use with a marker pen.

What rotary table do you have Larry? If it has dividing plates then you'll find it quite straightforward, if not then you might want to look at something like a division master to make the dividing easy (fool-proof, really). Also some rotary tables can make it hard to cut smaller gears because the machine fouls the table or chuck. One solution is to mount the blank on a shaft to bring it further out but you quickly find that you need to knock up a tailstock support in order to avoid chatter or deflection issues.

I work out my increments whenever I have to cut a gear (not many, but quite a few to do). Using tables would be OK, if they could be trusted, and it is not difficult to work out from basic principles.

I reckon the most important thing, when starting to cut gears, is to list every separate move for each tooth operation – and follow it religiously! That, or practise, practise, practise until every operation is imprinted securely in your brain. It only needs one thing missing and you may well be starting again. A bit like screw cutting – strict repitition is the name of the game.

You might find that plastic blunts your HSS cutters as fast as cutting steel. Some types can be surprisingly abrasive.

Also, getting a satisfactory finish on plastic may require a sharper cutter.