13DP Gears or Gear Cutter

Agree with John Stevenson and Howard Lewis that a "somewhere near" gear in delrin will almost certainly be more than adequate. Especially as the mating gears are almost certainly worn to some degree and therefore of less than perfect tooth form anyway.

If you do want them a bit better maybe the shaper method could be used to shave the gear teeth to almost the true form. As you already have a gear to start with it can be self indexed for automatic rotation using a strip of two or three rack form teeth engaging opposite the cutter. I guess for absolute best results you'd need to go round twice as for the first half turn the rack will be engaging in slightly wrong shape teeth. Presumably creating a small error when the teeth on the opposite side of the gear are shaved. Second time round pretty much all of the error should have gone.

Clearly way overkill here but possibly worth considering if inexpensive nylon or similar moulded gears can be found of suitable size and strength in the right tooth numbers but wrong form. Probably less trouble than setting up to cut from scratch and maybe a simpler technique for the neophyte who has no previous experience of gear cutting.

Clive

HPC at Chesterfield list Mod 2 gears in Nylon off the shelf, also list Tufnol if you want to use the cheque book engineering approach and get running faster ?

"Keighly, land of the living dead." Worked there for years, 1000 reasons why you couldn't do something and not one why you could, bit frustrating after all the engineering excellence that once came out of the town. Prince Smith and Stells, Landis Lund and of course DSG.

Yorkshire manufactured Textile machinery, Hmm, nothing to do with buying the cheapest parts, One that I worked for in Cleckhuddersfax had it's own range of shaft sizes and bore dimensions for gears and chainwheels. This ensured that competitors gears etc. wouldn't fit so the customer had to come back to us for replacements so the size of the gear which "May Be Metric" ain't necessarily so, more than likely to be a silly b***er size for this reason.

Regards Ian.

 Worth a try, there's an Industrial museum in Bradford and also Leeds that contain Textile machinery exhibits, may be worth a phone call to check if they have the specific machine.

Edited By Circlip on 27/04/2017 12:25:58

Is the large gear in the picture part of the same set? Measuring it would be less affected by any slight error in the original blank diameter and perhaps confirm the CP size suggestion.

They might have used UNC at that time if they had bought up some war surplus nuts or threading tackle.

When did the company fold? There could be some of the workers still around town who might even have made the specific loom.

If it is a museum piece in which case some effort to use cast iron would be preferable or are you trying to compete with the Indian weavers post brexit?

Hi all,

Solved it! Managed to get hold of the original drawings for the change wheels and they were indeed 1/4" CP. Well deduced. Going to a have a think now about the best way forward. I don't need it immediately, so I have the luxury of a bit of thinking time. It even seems possible to make your own cutter. Got the book and so very helpful instructions emailed over. So lots to go on!

Thanks for all your help everyone, really appreciated.

James

Firstly a good call by Niel A on the 0.25" CP form.

Circular Pitch isn't used much nowadays and even when it was it was usually used on linear movement.

DP always has Pi somewhere in the calculations but CP is a fixed linear move.

Ideally racks on machine tools should be in CP as then the hand wheels will relate to proper numbers. a 16 tooth pinion in 0.25" CP will move exactly 4" per rev.

Anyway to get back to the original problem. If James wants to make a cutter using the method outlined in the Gears and Gear cutting book then the following diagram should help.

The red which is hard to see as the green overlays it is one tooth of a 37T gear @14.5 PA and 0.25" CP or 12.5664DP the circle on the left is how the size was drawn using two chords on the curve to find the centre and mirrored to the other side.

So James wants two buttons at 0.700" diameter, spaced at 0.799" apart and a blank cutter of 0.250" wide.

Once the buttons come into contact with the edges of the blank he needs to infeed 0.224" to form the shap but when cutting the gear he only needs to infeed the cutter 0.175" deep.

This is a slightly different way to how Ivan Law does it in the gears book. He touches the OD of the buttons on the face of the blank and then moves across, then feeds in.

The method above is the one devised by Grant in Victorian times and resurrected by Unwin in the 1980's.

Thank you so much for this John, really helpful! Looks like it's going to be an interesting project.

James

You've averted a looming disaster!

IGMC

Neil