Tooth Angle for the Myford Bull Wheel Indexer device

Advert

New Replies

Report Bug

Help/FAQs

Tooth Angle for the Myford Bull Wheel Indexer device

This topic has 15 replies, 9 voices, and was last updated 26 February 2025 at 13:56 by Michael Gilligan.

Viewing 16 posts - 1 through 16 (of 16 total)

Author

Posts
24 February 2025 at 22:23 #785588
Greensands
Participant
@greensands
I am interested in making up the Myford bull wheel indexer as described by Harold Hall but I am not sure of the optimum angle used for the single tooth detent. Has anyone had any practical experience wit this device and can suggest the required angle?
Advert

25 February 2025 at 00:53 #785603
bernard towers
Participant
@bernardtowers37738
60 tooth 20 dp profile shortened so it has a wedge action in the gear teeth oh thats 14 1/2 deg profile but not that important.
25 February 2025 at 02:51 #785607
Chris Crew
Participant
@chriscrew66644
Not sure if the one I made is of the Harold Hall design because I just copied one a late friend had made, but just make sure it engages radially with the bull wheel. Obviously, it is only suitable for S7 or ML7R lathes that have a 60 tooth bull wheel because the ML7 bull wheel has an odd number of teeth. I marked the bull wheel teeth with different coloured dots at 2, 3, 4, 5, 6, 10 & 12 although I probably have only used the first four divisions available in practice. 15, 20 & 30 would be more easily available just by counting the teeth. Again not sure if HH suggested doing this as I have not seen his design.
25 February 2025 at 07:07 #785613
Diogenes
Participant
@diogenes
I think you should aim to get double line contact in the lower part of the gullet, and leave some clearance off the higher part of the shoulders – greatest strength and resistance to slipping will both be found nearer the root of the tooth.

If you try and establish anything greater than ‘double line contact’ you risk uncertain repeatability.
25 February 2025 at 07:17 #785614
DC31k
Participant
@dc31k
On 25 February 2025 at 07:07 Diogenes Said:

greatest strength and resistance to slipping will both be found nearer the root of the tooth.

There are not many good indexing devices around where the indexing mechnism also forms the locking mechanism.

The pin in the bull wheel is to establish position, not to resist any cutting forces.
25 February 2025 at 07:51 #785619
Michael Gilligan
Participant
@michaelgilligan61133
On 25 February 2025 at 07:07 Diogenes Said:

[…] If you try and establish anything greater than ‘double line contact’ you risk uncertain repeatability.

… and therefore: Our word for the day is Kinematics

and the options of using a rounded [or even a ball-ended] plunger are revealed

MichaelG.
25 February 2025 at 09:57 #785640
noel shelley
Participant
@noelshelley55608
Make a 30* wedge and file back until it no longer bottoms, this will give contact top and bottom of the teeth and SHOULD be repeatable. Noel
25 February 2025 at 10:34 #785643
Geoff Rogers
Participant
@geoffrogers81118
Have a look at G H Thomas’s book Workshop Techniques. I think it covers this matter quite well.

Geoff R
25 February 2025 at 10:43 #785646
John Haine
Participant
@johnhaine32865
The Myford headstock doesn’t have a spindle lock so the detent will have to hold it against any cutting forces.

Also the big-bore Myfords have a 65t bullwheel IIRC so pretty useless unless you want 5 or 13 divisions!
25 February 2025 at 13:15 #785689
Michael Gilligan
Participant
@michaelgilligan61133
On 25 February 2025 at 10:43 John Haine Said:

The Myford headstock doesn’t have a spindle lock so the detent will have to hold it against any cutting forces. […]

Yes … a point worth noting, John

Fortunately, the time-honoured work-around [*] of wrapping a cord around the chuck and hanging a weight on the end serves very well for many jobs.

MichaelG.

.

[*]

I suspect that Noah used this when building the Ark
25 February 2025 at 14:24 #785713
Greensands
Participant
@greensands
The application I have in mind is use with a cross slide drilling attachment for which I would have thought the double line contact approach as suggested above would be quite adequate.
25 February 2025 at 17:00 #785783
John Haine
Participant
@johnhaine32865
The most important aspect is probably to ensure that the detent is solidly held in the same position each time without any shake or play; and presses firmly into the tooth space (possibly using a clamp screw to press it in). The detent might be mounted on the end of a fairly substantial steel strip (say 2mm or so), long enough to have some spring. The other end could then be clamped firmly somewhere convenient.
26 February 2025 at 12:45 #786064
bernard towers
Participant
@bernardtowers37738
The main problem with His indexer is that the belt cover won’t close and you have to drill and tap the head stock.
26 February 2025 at 13:00 #786077
Michael Gilligan
Participant
@michaelgilligan61133
This old thread is worth a look:

https://www.model-engineer.co.uk/forums/topic/myford-bull-wheel-indexing/

MichaelG.
26 February 2025 at 13:40 #786098
Greensands
Participant
@greensands
Yes, but if I am not mistaken, his drawings do not indicate the angle for the detent tooth
26 February 2025 at 13:56 #786100
Michael Gilligan
Participant
@michaelgilligan61133
On 26 February 2025 at 13:40 Greensands Said:

Yes, but if I am not mistaken, his drawings do not indicate the angle for the detent tooth

Please see my earlier post

https://www.model-engineer.co.uk/forums/topic/tooth-angle-for-the-myford-bull-wheel-indexer-device/#post-785619

MichaelG.

.

Edit: __ if clarification is required … a single-curvature will make line-contacts, and a ‘ball-end’ will make point-contacts.
Author

Posts