Gear cutting

Hi Everybody,

I want to pick your brains regarding the above subject. I am new to gear cutting,so I wish to ask before I screw things up.

This is what I have

Set of cutters

Lux mill

Mild steel blanks [to begin with ]

Rotary table.

This is what I dont have;

Experience

Expertise

.What I would like to know is

A What spindle speed should I be using

B When cutting,should I take small cuts or go to full dept.

C What feed should I use

I know that this is old hat to most of you,but it,s new ground to me and I would be thankful for any advice.

Thank you in advance for your help

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

Thanks very much Brian,that,s what I wanted to know. I do have power feed for the left to right table movement [x ? ]

I forgot to mention that the cutters are 1,5 Mod,though perhaps this is not important.

I shall have a go at it as soon as I can set up and will keep you posted.

Thanks again.

Larry,

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!

Posted in error........

Edited By David Standing 1 on 19/10/2018 17:48:36

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

Larry,

I have recently finished cutting a set of gears for my 6" traction engine. These were with 4 DP cutters so a fair bit to come out on each tooth, gears were cast iron so as others have said cut in a single pass. Cutter speed worked out on 90 fpm (which should hold good for steel) and was as stated around the 100 rpm. One thing I do when cutting gears is scribe a line at every division and number them with a sharpie. I then clamp a scribing block to the table aligned with the line, gives a quick visual check of position each time you index - and saved me some grief a couple of times during the job! It's easy to get distracted.

Paul.

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

You didn't say what the gears are for but avoid steel unless necessary because of the strength needed for the application. Steel will blunt your cutters so it certainly isn't a practice material. Various types of plastic and aluminium are enough for change gears. Brass of course for clocks except of course pinions where you do have to go for steel.

If cutting thin material make a sandwich with discs of plastic or wood or aluminium just below tooth depth for support and even full height and cut it too.

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.

Some tooth counts csn be achieved with a spin indexer which will typically allow setting to each whole degree. If you have rotary table but no dividing plates then using a spreadsheet to print off a table of angles for each position will allow accurate setting.

Martin C

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.

Hi Bazyle,

Just thinking about your idea of using plastic. What type of plastic should I be looking for? As you say,it might be kinder to my cutters than steel. For some reason steel was my first thought.

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

Larry,

PVC is good and won't blunt anything

Brian

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

Actually ega it just involves higher cutter speed, the cutter should be sharp enough if correctly sharpened.

It's all a bit artificial really, PVC gears aren't a lot of use except to prove that all the parameters in making them have been set correctly and if there has been a cock up somewhere, the cutter won't need attention afterwards.

Get it right and the boost to morale is invaluable, especially as this is a first attempt for Larry

Brian