Gear cutting

Not sure if this is the right place,but here go,s anyway.

Some of you may remember that I asked for advice on gear cutting. The response was all I could have hoped for,and I thank everyone for their time and interest.Since then,I have made my first attempt at the subject and thought that you might be interested to know the results.

First off,I used a piece of Ali,which was to hand 63x20. This was big enough to give me a 38 t gear [1.5 mod ]. Cut it out with hacksaw/angle grinder,drilled it 12mm and mounted it on an arbor nothing fancy !then turned it to size and set it up on the mill.

Set the cutter to just brush the blank,then moved the spindle to one side while I set the dept of cut using my dial gauge. I had already been around the course to make sure that the setup was right,so I was happy enough to begin cutting. To my surprise,it went very well,no real problems,although I did feel that not all the teeth were cutting.I seem to remember that someone else remarked on this some time ago. This may be due to the cutter bore being slightly off center or the holder not being quite true.I will get a better holder for next time.

The cutting went very well and I was quite satisfied with the result [for a first effort,anyway ] Since I did not need a gear of any particular size,this was just an exercise,part of the learning curve.Since I had enough scrap Ali left over,I made a smaller gear 20t just to try it..Both worked out well,just trying to work out how to cut a slot for a key [drill and file ? ]

While looking at the range of teeth the cutters can deal with,I wondered that No1 can cut 135 to a rack ! Can you cut a rack with a mill,or am I reading this wrong ? dont really how you could move the workpiece. Perhaps not.

Again,my thanks to everyone,not forgetting Brian for the help and advice.

It has been a most satisfying experience.

,

You can cut a rack in a vertical mill, moving the cutter and holding the blank vertically - just not a very long one! TBH I have no idea how they make long racks.

Up to a point, and according to length, they could be done on a horizontal mill; in the motor industry I believe they are cut using broaches or at least used to be.

Right angle attachments are available for some machines. Then very easy to cut a rack to full length of the table long travel.

Here is one one on epay for a bridgeport

**LINK**

Presumably, on a Vertical Mill, a longer Rack could be cut using a formed "end mill", and indexing the Table by the Pitch. Probably slow, and repetitive, but not impossible. Being a rack, the cutter teeth would be straight sided (a gear of Infinite radius).

No doubt Ivan Law's book will provide the necessary detail for such a cutter. to be made.

With this method, by offsetting the work at an angle, a Helical rack could be produced, if so desired.

Just musing, have never needed to do it; yet! (Biggest gear yet cut was 100T)

Howard

Edited By Howard Lewis on 31/10/2018 17:29:12

Hello Larry,

Norman and NDIY are both right, racks are best cut with a right angle head on a horizontal mill so that you can get the cutter down close to the table. I'm sure there will be a U tube video showing it being done.

The tricky bit then is to index the work correctly so that the teeth on the rack are all correctly spaced.

Ideally the driving slot is cut with a broach pushed through from one side to the other, but you can do the job on a lathe with a tool held in a bar and used that to shave off a bit at a time with the tool held horizontally and moved outwards by the cross slide between cuts. Hemingway sell kits that allow you to push such tooling through like a rack operated tailstock which saves a great deal of cranking of the carriage up and down the bed. You do save a bit of work too by opening up a suitable size of hole through the blank; it is best if you have drilled that before making the bore hole.

Did the gears you made also mesh together nicely? If so well done for a first attempt

Regards

Brian

Here is a 20 dp rack cut on my Warco mill ,as is usual with these sort of jobs there is some parts that need to be made to enable this to be done .As the machine is part cnc the spacing and driving the cutter through is done with a small cut file ,the cutter depth is set on the knee.The rack has about 160 teeth and is about 25 inches long.

There is a quick and easy way to do keyways in shorter lengths , just clock the centre of the hole on a mill and plunge an accurate sized cutter to the size of keyway you want down in steps until wide enough for enough key engagement , much quicker and less fiddly than doing it in a lathe , yes the top of the keyway is round but in most instances this doesn't matter, you make the height of the key to just fit in to stop lifting , heres a pic of a pulley with a 3/16 keyway only took 10 mins to set up and do.

Edited By Kettrinboy on 01/11/2018 09:03:16

While kettrinboy’s solution may be valid for most hobbyist jobs, l have recently used the hand shaper to cut the slots.

Part-machined, with a slot mill, would help in steel... I prefer a more completely fitted key, but if the key is tight in the shaft it will not move and fret the pulley slot. Loose keys are not good news!

That's a brilliant way to put in a keyway, you learn something new every day. Thanks for that Kettrinboy.

Doug

Whilst in theory - I could turn the vertical head on my Victoria horizontal through 90 degrees to cut a long rack - in practice I wouldn't have enough clearance to use gear cutters held directly in it's spindle. I'd need some kind of secondary spindle, as John has produced for his Warco vertical mill. Not sure how I'd do that on mine however (at least simply) - interesting problem though...

BTW - always like a photo or two to make things clearer. Can you show us the other side of your set-up please John?

Regards,

IanT

Hi Ian, The first photo shows the drive to the spindle ,as you can see the head is swung around by 180 deg and the drive gear is mounted to the main spindle.A reduction gear arrangement is clamped around the quill ,this originally was going to form part of the mechanism for a mechanical gear hobbing unit on the mill but was abandoned in favor of an electronic hobbing unit made by Richard Bartlett (Compucut).The keyed driveshaft transmits to the spindle via the bevel gears .The hardened spindle runs in bronze bushes in the spindle housing,the cutter is home made as in the book Gears an gear cutting by Ivan Law and at 1 1/2 inch diameter protrudes just enough below the edge of the spindle block to clear.The spindle block as can be seen in the earlier photo is held on the rear of the head column ,a diagonal brace connects to the main column and provides considerable support  to  the mounting.

The second photo shows a close up view of a shorter 20 DP rack.The vice provides the main support ,the two blocks either side are secured to the table with T nuts and milled level in situ to provide the support either side of the vice jaws.

Edited By John Pace on 01/11/2018 10:55:47

Like Ketterinboy, I used a similar method to locate the R8 arbor to the top of the boring/facing head that I made, as I don't possess a broaching kit. Slightly differently, though, I used a piece of silver steel rod instead of a "normal" square key to provide a positive drive, cutting a semi-circular groove in the arbor with a ball-end milling cutter and a matching one in the boring head body. The short length of silver steel fits snugly in both parts and the grooves can be seen ( just ) in the pictures below.

Edited By John Hinkley on 01/11/2018 12:06:25

Thank you John (Pace) - very ingenious!

Regards,

IanT