How do I do this?

Hello All,

Pretty simple question (I hope) - how do I machine this kind of hole into the end of bar? I have a lathe with a vertical slide so I can do the odd bit of light milling but do not own a stand alone milling machine. It is to go on a motor shaft.

Thanks

Its not possible to machine the desired shape in a bar end. You could machine the hole and then make a round segment to fit in the portion thats left.

Are you trying to make the shaft attach to the shaft, is so why not make it fully round and tap a hole through onto the shaft to stop rotation?

Bri

Thomas,
There are ways to create the profile you have drawn but you need some nifty kit like a spark eroder so for all practical purposs Bri is right.
In most instances the flat on the motor shaft is to prevent any burr raised by clamping screws from allowing you to remove the collar from the shaft for servicing etc.
If you need your collar to slide on the motor shaft without rotating you could try Bri's fabricated segment that is screwed through the collar section.

You might make such a segment by turning a 12.5mm diameter onto a stub end of steel and then milling a 10mm slot across the diameter to a sufficient depth to create two segment bits, cut these off the stub and then fix one of them to the inside of the collar which would have a plain round 12.5mm hole to fit your motor shaft. With the segment fixed to the collar you can arrange the assembly to be a sliding fit and still provide the drive and angular lock required.
Possible , but a lot effort if it's not really necessary.

Bob D

Edited By Robert Dodds on 27/02/2015 22:24:30

feel free to shoot down an outrageous idea from a newbie. But if you bore a round hole, then create a temporary dam to the level needed and fill with a mix of slow epoxy and fine filings it'd overflow and settle to the point needed. Dress off any overflow...???

I've seen them done with a homemade broach, its the same shaped hole that you find on the prop driver of a lot of model aero engines.

When you say on the end of a bar is it a blind hole if so how deep and also what is the bar steel, aluminium, etc.

One way to machine would be drill 10mm then setup in a rotary table with a small dia cutter and mill out to 12.5mm and a straight cut along the top. This would leave a small radius where the flat meets the curve depending on the dia of the cutter which could be planed out if a blind hole or filed if its being parted off.

J

Yeah I see it now sorry. So are you making a mating female shaft extension or something?

Sorry Bri I didn't read your answer I'll let you go for it.

Edited By Jesse Hancock 1 on 28/02/2015 07:50:19

Edited By Jesse Hancock 1 on 28/02/2015 07:54:25

Hi Thomas,
I would bore the hole to diameter (12.5mm) I would then mill a flat on the bar down to the level of the required flat. (5 mm from centre) I would then silver solder (Or possibly weld.) a flat plate across the milled flat. Then finaly re machine the outside of the bar to diameter. I used this method years ago to make a "D" shaped key to fit a water shut off valve that supplied our house. This did not need to be precise so I just cut the flat with a saw and welded the flat plate on.

Les.

Or fit a grub screw to the outer shaft.

Neil

Drill hole, broach wide shallow keyway, fit key, solder in.

In production I think a punch or broach would be used, or if large enough a profiling head.

Hi Thomas,
Another possible way to do this would be to use a rotary table mounted on a shaping machine. A variation on this idea would be with a tool mounted in the spindle of a vertical mill with the spindle locked in position and the workpiece mounted on a rotary table. This would only work for a through hole or if the inner end of the blind hole was bored out to the full diameter.

Les.

The only simple way I can see to do it, is drill the hole, then braze in a small slice of steel to form the D shape.

Ian S C

As you do see items like this there must be a way of making the hole.

There seem to be two options:

Remove most of the waste by drilling and then use one or more broaches. Making a few thousand a practicable, and affordable, method for one or two hmm.

Or drill out most of the waste and file to shape and size, In olden days I guess apprentices practiced doing this and got good at doing it :will need a lot of skill. A home made single stepped broachy thingy might be usable to bring to final size.

Can't think of a reasonable method if you want it as a blind hole -- on wit the grub screw!

JOHN

Hello All,

Thanks for the overwhelming amount of responses! So either broaching/scraping or removing extra material in another axis and fitting in the square part separately.

Yes, this is to go on an existing electric motor with this shape already on the end of it's shaft - it is also too short to cut a keyway or any other hole in it as the motor would foul onto the chuck.

I could do a simple grub screw job but the mechanism it is powering will be under a lot of resistive torque (is that a term??). In other words the motor shaft needs to have a really good grip on the arbor that requires this odd hole, otherwise it may fail and I am unsure if a grub screw is up to the job.

Cheers

Edited By Thomas Gude on 01/03/2015 13:47:36

A grub screw is what is intended, the flat is a fairly standard addition to the shaft, the flat stops the shaft from getting marked. The screw does not drive, it increases the friction between the shaft and the pulley. If worried about the torque transmitted use Loctite or similar, but you should not need it.

Hi Thomas, I've seen a "simple grub screw job" on this type of shaft in a few industrial lab machines, they work better than you might imagine, simply because the bore should be a reasonable good fit on the shaft in so much they would be a slight press on fit. With a good fit on th shaft, the grub screw's real job is to hold the opposite side of the bore in the pulley or whatever in tight contact against the shaft and give good frictional power transfer from shaft to pulley. the idea is not so effective on a loose fit between the two because there is more of a point contact, and you can get a side to side oscilating movement, which will eventually work loose.

Regards Nick.

If you are really worried, make a keyway opposite the flat.

Neil

I've done it this way with motor pulleys a couple of times.

Drill & ream the hole and mill a slot as shown in the pictures below.
Insert the orange coloured piece of plate, making sure that it's a good tight fit in the slot. Secure with a grub screw if required.

Martin.

Edited By blowlamp on 01/03/2015 16:47:51

Hi Martin (blowlamp),
That's a very nice solution to the problem and relativly easy to achive.

Les.

PGK

Your idea is quite feasible, I have successfully used JB weld to repair a stripped flymo shaft, this year will be it fourth season since it was repaired. Quick and easy and saved loads of time stripping the engine down and cutting a new keyway, just have to keep a keen son from mowing the orchard again!

Neat!

Andrew