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Magneto coupling taper

99Panhard

Stainless
Joined
Feb 22, 2006
Location
Smithfield, Rhode Island
I'm thinking of making an impulse starter for my 1910 Mitchell from a set of patent drawings of one that was invented around 1906. The major stumbling clock is that it has to have a tapered hole in order to fit the magneto. The taper is one originally used by Robert Bosch and later adopted as the SAE standard. Here's the pages from the SAE handbook describing it... The specs for automobile magnetos are on the first line of the chart.

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I was thinking of a tapered end mill but I can't find one with the correct 11.5 degree taper. Is such a thing available? Or, if not, what might be a good way to go about this.
 
Can you bore it on the lathe with the compound set to the correct angle and or test fit and adjust to get the right fit on the shaft?
 
I think the finish from an end mill is not going to be good enough for a nice snap on taper fit.

Doing it on a lathe will allow you to really tweek in the size and angle

If you need to do some ops on a mill the part may end up being 2 pieces

It occurs to me that if it became an SAE standard, that you could probably buy and modify something so cheaply it would be silly to buy any tooling at the price
 
Those pages are from the 1926 SAE handbook. It has been a long time since cars had this type of magneto so unless I'm missing something, there is no currently available part that comes close. I've been looking - and continue to look but so far it's been unsuccessful.

It's too small for me to bore, at least with the boring tools I have. I may look into that but I'd have to buy some tooling in any case.
 
I've had custom tapered reamers made, and had existing tools modified to match automotive tapers for one offs. Tool sharpening shops can do it if they are willing.
 
For making one or a small number of parts setting the lathe compound and boring as suggested by Grig would be the least expensive option .
You can use trig and dial indicators to set the angle to 5.75 degrees rather than trying to guess at the graduations on the compound base or if you can get the magneto shaft in the lathe and pickup the taper from it with an indicator on the compound.
You may have to invert your boring tool and cut in reverse or indicate from the back side of the shaft so you can bore the taper in the usual way .

One way to cut the taper using a tapered end mill is to choose one with a larger taper of 6 or 7 degrees per side as available and grind it to the 5.75 degrees / side.
It is usually easier to reduce the large end of a tapered cutter with a larger angle like 6 or 7 degrees /side to a smaller angle rather than to increase the angle of a 5 degree / side or 10 degree included angle cutter.
It avoids clearance issues if you have to remove a lot of material near the tip of the cutter
It depends what cutters you can find available from stock for a reasonable price.
If you have a local cutter grinding service that does good work they should be able to modify it for you without too much trouble .
I have found that many sizes are not available for quick delivery even if they are shown in a catalogue or on line .
Some are shown in this link
http://www.awardcutter.com/Products/HSS & CO Sizes.pdf
Award is one U.S.Maker that I know of and there are others.
Award Cutter Company Inc. - Products

Regards,
Jim
 
Same in 1938 SAE handbook - but there are two differing small ends of taper - .441 and .472" (on edit - which I see is on the second chart)

I'll see if any of my tapered end mills is a suitable regrind candidate

Also can be done with tilting rotary table and a STRAIGHT end mill
 
T

It's too small for me to bore, at least with the boring tools I have. I may look into that but I'd have to buy some tooling in any case.

For a .472 or so small end, try using a 3/8 endmill as a boring bar, just align one flute with the bore centerline.
 
I do have an inquiry in with the cutter sharpening place I've used in the past to regrind a 1" end mill with a 1/4" radius. I have't heard back from them but It's good to know it's possible.

How close would I have to get for it to be a candidate for resharpening?
 
I do have an inquiry in with the cutter sharpening place I've used in the past to regrind a 1" end mill with a 1/4" radius. I have't heard back from them but It's good to know it's possible.

How close would I have to get for it to be a candidate for resharpening?

I'd rate is easier, faster, and cheaper in money as well as time to make a single-flute reamer, along the lines Mud suggested. Second-cousin to "D" drills and reamers, same clan and tribe.

Because we have done. They suck at clearing chip. BFD, go slow, double the ration of patience you mix with the cutting fluid, and apply the air.

Think on it. Size and taper can be dead-nuts whatever you need it to be, yet you don't even have to divert time to leave the shop to go-fetch nor maybe even to go-order. Works good, it is good.

Not as if we have to use those for mass-producing ten thousand successive identical parts. You might make but a proof test, the one, plus one spare - and done4ever.

Even ignorant HCS, torch hardened, will work a treat for THAT.
 
I think for a one of job I would try the D-bit solution suggested by Limy Sammy and try it on a piece of scrap material first.
It didn’t occur to me when I posted before.
I have modified existing tapered end mills and made small D-bits grinding them out of hardened Drill blanks depending on the job at hand.
If you don’t have grinding facilities making one out of drill rod and hardening it with a torch would be the quickest way.

In modifying taper end mill you can probably get away with removing almost 1/16” diameter from the large end but taking more than 1/32 dia. on a small cutter means that you might have deepen the flutes a little.
If the tip is too small they can be cut off back near the required size and a new end cut but that starts to add to the cost.
The key is to find a cutter that is already close in size to what you need leaving only a little work to bring it to the right angle.
Also a lot of tapered end mills come with 3 flute so it measuring them is not as easy as with 4 flutes .
I have had to make bushings to gage the sizes of the tips on some 3 flute cutters an with some another bushing for the large end depending on the job.
I have attached a photo of some end mills I did to modify a hole on an spindle to fit a tire rod end with a different taper that was a degree or two different from the previous one .

This was for a special job and the tool was used to re work many parts.
P.S. didn't see Thermite's post when I started.
Regards,
Jim
 

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Couldn't you use an impulse from another magneto?

The one I have won't fit. Besides, I like the idea of using one that was invented in period. All the other I'm familiar with date from WWI or later.

What's a "D" bit?

And... a single flute reamer?

Remember, I'm a totally self-taught amateur who has only set foot in a real machine ship a few times.
 
Here is a 1/4” dia. tapered single flute cutter or D-bit from my collection but not made by me from a piece of hardened drill blank.
Taper can be ground on something like a spin index fixture on a surface grinder if a cutter grinder is not available and then ground in half .
They can be made with a cm relief on the curved side that will cut better but round ground in half should be Ok for a few pieces.
Jim
 

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Here is a 1/4” dia. tapered single flute cutter or D-bit from my collection but not made by me from a piece of hardened drill blank.
Taper can be ground on something like a spin index fixture on a surface grinder if a cutter grinder is not available and then ground in half .
They can be made with a cm relief on the curved side that will cut better but round ground in half should be Ok for a few pieces.
Jim

Dead flat works fine. Even a slight crown is OK.

Made them for years,"BMMA" (Before Milling Machine Arrival) by doing the diameter, end shape, any taper if need be - on the lathe, entire flat from scratch with a hacksaw cut, hand files, and bench grinder - finish with hand-stoning.

No need to "revert" to that if you are better-equipped, but with exactly one flat they really are just that easy and simple.

Oh. BTW. Also bi-directional, so if your spindle is reversible, there's double the cutting-edge life for one ration of material and labour.
 








 
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