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View Full Version : Can anyone explain how to use this indexing device please?



The Artful Bodger
07-24-2012, 12:14 AM
Can anyone identify, recognise or even explain this indexing instrument?

http://farm9.staticflickr.com/8023/7634617632_dcb00f98f0.jpg (http://www.flickr.com/photos/25239206@N06/7634617632/)
IMGP9971 (http://www.flickr.com/photos/25239206@N06/7634617632/) by aardvark_akubra (http://www.flickr.com/people/25239206@N06/), on Flickr

It came with my Drummond 3 1/2" lathe of about 1908, I am sure it is not original to the machine and it has a couple of flaws indicating that it is shop made item. The centre bore diameter and the two holes indicate it is intended to the mounted on the spindle or mayb e one of the change gear positions (which presumably would increase the range of choices for those with suitable mathematical skills).

http://farm9.staticflickr.com/8012/7634610578_e6dffb916e.jpg (http://www.flickr.com/photos/25239206@N06/7634610578/)
IMGP9968 (http://www.flickr.com/photos/25239206@N06/7634610578/) by aardvark_akubra (http://www.flickr.com/people/25239206@N06/), on Flickr

It has a number of circles of index holes, 3, 4, 6, 8, 12 and 60. These strike me as having rather a lot of redundancy but maybe there is something I do not understand.

There are also parallel rows of holes in two places, one of these rows is obviously not on a radial line, again somewhat puzzling.

The front(?) of the instrument has a moving cursor complete with an extension which presumably bore against a fixed point on the lathe. Clearly this cursor is intended to be used with one of the parallel lines of holes as they dont quite line up on the other.

http://farm9.staticflickr.com/8027/7634612770_86fa8aebaf.jpg (http://www.flickr.com/photos/25239206@N06/7634612770/)
IMGP9969 (http://www.flickr.com/photos/25239206@N06/7634612770/) by aardvark_akubra (http://www.flickr.com/people/25239206@N06/), on Flickr

The rear(?) of the instrument has another movable arm that can be locked to any hole position. This arm is fixed to the hub and provides a means of fixing the position of the disk in relation to the lathe spindle. The non-radial line of holes line up with this arm.

http://farm8.staticflickr.com/7113/7634615390_2a19faa056.jpg (http://www.flickr.com/photos/25239206@N06/7634615390/)
IMGP9970 (http://www.flickr.com/photos/25239206@N06/7634615390/) by aardvark_akubra (http://www.flickr.com/people/25239206@N06/), on Flickr
I will be very grateful if anyone recognises the design and can point me to some information that would help me to understand how this device is used as the complexity leads me to believe it can be use for much more than multiples of 6 and 45 degrees.

Thanks

Paul Alciatore
07-24-2012, 04:01 AM
I can not shed much light on exactly how it was to be used, but unless additional gearing is used (like the change gears) it IS limited to multiples of 6 and 45 degrees.

Those extra rows of parallel holes would/may provide some additional indexing positions but I do not see any clear way of knowing what the angles involved would be. Some measurements and a bit of trig would be needed.

I suspect the person who made it added the redundant hole circles just for convenience when making fewer divisions.

willmac
07-24-2012, 05:49 AM
I can't suggest anything really specific without seeing a bit more of the lathe, but I do use indexing based on change gears quite a bit and could guess how this might be applied. In the photo below, I am setting up to graduate a micrometer thimble using a graduating tool in the toolpost. The thimble needs 1s, 5s and 10s marking. It is really easy to make a mistake when you do this, but an indexing disk suitably marked up and attached to a gear can help to reduce the risk. In this case I use a 40 and a 20 gear train to get a 2:1 ratio, with a 50 tooth gear acting as the index wheel. The Tippex marks are for 5s and 10s. The index wheel goes around twice for the complete thimble. I have a detent pin that locates in the indexing gear. The handle in the spindle is to rotate it.
http://i122.photobucket.com/albums/o248/moorbrook1860/13042011.jpg
I could imagine your index plate in place of the index gear and a the arm being limited in rotation by a separate stop. You then relocate the arm and make the next indexing. Even with the limited and partly redundant hole pattern you can get a lot of angles from your wheel if used in conjunction with some simple gearing.

The Artful Bodger
07-24-2012, 06:08 AM
Paul, I think the two parallel rows are just holes for the front and the back arms. One row of holes is not on a radial and that lines up with the back arm which has its holes off the radial to match. It all seems a bit more complicated that what is needed for what we think it can do!

Bill, the device can be put anywhere in the gear train, on the spindle or geared to it. The lathe would have originally had change gears that are multiples of 5. If you wanted to cut metric threads you would need a 26 or a 63 tooth gear, so for example, if you wanted to cut either gear I dont see how you could go about it with this device and my brain goes numb when I try to figure out what gears, of the available set, would be needed!

I find it very strange that this device has two arms and the movable disk yet seems to have such a limited range of indexable arcs available.

oldtiffie
07-24-2012, 06:34 AM
At least one of the problems with these "indexers using the gear-train" is the gearing back-lash between the indexer and the chuck or what-ever else the part being indexed is held in or on. You might be surprised at how much back-lash there is.

Barrington
07-24-2012, 06:47 AM
Is the rear arm perhaps fixed with respect to the hub, with the disc then free to rotate if the screw is removed ?

If so it might be to used to offset the disc and hub in 1 degree (?) increments.

That wouldn't explain why there are two sets though.

Cheers

.

The Artful Bodger
07-24-2012, 06:49 AM
Thats if one does use a gear train, I thought there might have been some cunning way of using this device direct on the spindle for more that x6 and x45 degree arcs.

There is heaps of backlash on this lathe but it is easy enough to move the studs for fairly tight engagement, which does not eliminate backlash entirely.

I have not tried to calculate all the intervals if all the change gears combinations were used. The gears for this lathe go from 20 to 55 in steps of 5 (teeth). Up to four stages of gearing could be used so thats a lot of combinations!

willmac
07-24-2012, 06:56 AM
At least one of the problems with these "indexers using the gear-train" is the gearing back-lash between the indexer and the chuck or what-ever else the part being indexed is held in or on. You might be surprised at how much back-lash there is.

Yes, of course there is backlash. You need to deal with it in a consistent way and then you can get very reasonable accuracy with this method. When I first started using this approach I worried about it and used several complicated methods to get around it. One example is wrapping a cord around the chuck and then hanging a weight via a pulley. This is awkward to say the least and I now find that I can get very good results by keeping a consistent hand pressure on the hand crank against the detent pin. It is fortunate that my ML7 is mall enough that I can use one hand on the hand crank and the other to operate the graduating tool, without any problem. This is fine for graduating a dial, but might not be for gear cutting.

oldtiffie
07-24-2012, 07:01 AM
As the indexer is registering in thegear trin you will need to be sure that there is a 1 : 1 ratio between the gear and the chuck else if itd not you make gaet an unfortunate surprise - and have to work out a gear-train ratio to suit.

The best indexers are those that register directly on the lathe spindle/flange/chuck/accessory dividing plate.

The Artful Bodger
07-24-2012, 07:18 AM
I have not tried to calculate all the intervals if all the change gears combinations were used. The gears for this lathe go from 20 to 55 in steps of 5 (teeth). Up to four stages of gearing could be used so thats a lot of combinations!

Barrington, thats right, the rear arm is fixed to the hub, the disk and the front arm are free to move. I have tried to see how the two arms can be used to get more than 6 degree intervals and the best I can come up with is back 45 and forward 48 for an interval of 3 degrees.

One of those rows of holes really only matches the rear arm while the other row matches the front arm and they are 6 degrees apart but I cannot see any way of using these to get increments of less than 6 degrees.

I doubt I will ever use this indexer as I have a dividing head but there may come a time when I want to index something in this lathe.

The Artful Bodger
07-24-2012, 07:23 AM
The best indexers are those that register directly on the lathe spindle/flange/chuck/accessory dividing plate.

This one does that (it mounts directly on the spindle) for intervals or 6 and 45 degrees directly, and 3 degrees (by going back 45 and forward 8x6).

Barrington
07-24-2012, 07:41 AM
Barrington, thats right, the rear arm is fixed to the hub, the disk and the front arm are free to move. I have tried to see how the two arms can be used to get more than 6 degree intervals and the best I can come up with is back 45 and forward 48 for an interval of 3 degrees. I was suggesting that the screw position in the rear arm moves the disc 0,1,2,3,4,5 degrees relative to the hub, filling in the gaps between the 6 degree steps on the front arm ?

Cheers

.

Circlip
07-25-2012, 05:09 AM
Wonder if the original maker was into clockmaking? Divisions seem more suited to this application.
Regards Ian.

The Artful Bodger
07-25-2012, 05:20 AM
I was suggesting that the screw position in the rear arm moves the disc 0,1,2,3,4,5 degrees relative to the hub, filling in the gaps between the 6 degree steps on the front arm ?

Cheers

.

OK, I took another look and it is true, the rear arm can be indexed to 1 degree (by using the line of holes it does not line up with! If that makes sense!).

The Artful Bodger
07-25-2012, 05:29 AM
Wonder if the original maker was into clockmaking? Divisions seem more suited to this application.
Regards Ian.

Perhaps you are right Ian. As far as I can see we now have an explanation for indexing all 360 hole degrees.