|John Hinkley||05/04/2019 20:16:54|
738 forum posts
This project started as a way of getting the hang of the Alibre Atom 3D CAD program offered a couple of months ago in MEW. I'd tried a number of 3D packages before and never got to grips with any of them. Somehow and for reasons unknown, I seemed to "click" with this one. Once i got the idea of building up an assembly of parts in my head and put them together in a co-ordinated way, it seemed relatively simple to create the parts in the computer. To start with, I "made" a few simple objects and quickly moved on to more ambitious designs. Then I decided to actually create something that would be useful in the workshop, so I cast around for a tool or fixture that I didn't possess but was on the "nice to have available" list. Thus, this indexer was conceived. I decided that I would limit it to providing division by single degrees and not fractions of a degree. (To be honest, I thought I could do the former, but couldn't think of a way to acheive the latter!)
So, basically, the rotating part was a straight shaft with an ER25 collet chuck on the end - because I had one on a shelf. This had to be supported somehow, so I designed a casting. When I got a quote to produce two castings in aluminium, it was going to be the thick end of £200! Back to the drawing board - or rather the mouse and computer. It made sense to construct the tool in materials which are readily available from most stockists, so that's the way I went.
The collet chuck is mounted on two supports and runs in oilite bearings, the whole being mounted on a base plate.
Opposite the business end of the shaft sit two circular plates, the inner one free to rotate on the shaft, the other, outer one, keyed to it. There are 36 holes at 10° spacing on the inner side of the floating plate (what I called the "reference plate" ) in which a removeable detent engages, through the shaft support. On the other side of this plate are eleven holes, one at 12 o'clock (representing a zero degree position) a second at 79° and subsequent holes at 30° spacing proceeding clockwise.
The outer plate (I call this the "indexing plate" ) has a similar layout of (threaded) holes on the same PCD but at angles of 78° and 29° respectively.
This arrangement allows the holes to be rotated by one degree per pair of holes in much the same way as a vernier scale works. By using a combination of a selection of 10° and 1° divisions, any angle can be obtained.
I foresee its use in a number of workshop applications in addition to the usual ones. For example, in another thread posted this evening, I notice that a member requires assistance making a camshaft. Jason has suggested a method involving milling the profile in a number of stages by rotating the blank a few degrees at a time. Use this and it can be done in one degree increments, if needed.
By substituting a rotating handle, such as used on a cross slide advance screw, and removing the reference plate detent screw, it can be converted into a rudimentary rotating fixture for basic cylindrical grinding,
The possibilities are only limited by one's imagination.
Here is the prototype nearly finished. It's working but needs the graduations engraved and a couple of little tweaks before I'm perfectly satisfied with it. You can compare it with the Alibre output, above.
There are a few more pictures and brief construction details in my album ("A degree of indexing" ) should you want more info.
Edited By JasonB on 06/04/2019 06:52:01
|Michael Gilligan||05/04/2019 20:34:50|
13591 forum posts
Nice one, John
... Looks, to me, like a strong contender for the 2019 Stevenson Award.
|John Hinkley||05/04/2019 20:59:06|
738 forum posts
Thanks, Michael. Those blasted winkies are back. They don't appear when I use the iPad, only when I use the PC. Now it's too late to remove them.
|Neil Wyatt||05/04/2019 21:57:00|
16293 forum posts
|Chris Evans 6||06/04/2019 09:08:39|
|1442 forum posts|
John, If you make your own patterns I would expect a casting cost around a quarter of what you were quoted. Where in the UK are you based ? Good foundries here in the West Midlands.
|John Hinkley||06/04/2019 09:40:03|
738 forum posts
You are quite right. The quote I received was for two castings (in case I messed one up!) including the making of a pattern, itself £100. Then add VAT, delivery and so the price mounts up. I moved here to near Doncaster a year ago, so I expected to be within easy reach of a number of foundries. Unfortunately those whom I contacted for quotes did not respond - even one that claimed to specialise in one-offs. Companies like that don't get a second chance, in my book.
When we moved back to the Uk, I either sold or gave away all my wood working tools, which makes mould-making difficult. As it happens, I think the stock material route is a better solution. Even if it's not as pretty, it's practical, functional and reproduceable.
Neil - thank you for the winkie surgery. (Sounds painful!)
|jann west||06/04/2019 10:13:18|
|45 forum posts|
might be cheaper to just buy a 5c spin indexer and a 5c - er25 adapter
and a 5c - er25 adapter
Although not nearly as much fun
|1280 forum posts|
Probably not cheaper (than making your own) Jann - but certainly easier - yes.
However if you do make something along these lines, then you can bore the holder at lathe centre height and then it becomes a useful accessory for the lathe too (even if you do have a mill).
I have a 'Timmins' dividing head that is designed to fit both the Myford cross-slide and (turning it through 90 degrees) gives more clearance (e.g. height) on the mill. It has a Myford 'nose' and a MT2 taper - so I can also fit my ER32/MT2 collet chuck to it if required. I got it after I'd purchased a Spindexer which is still used when I need a larger 5C collet.....
Nice work John.
|236 forum posts|
What is the logic and maths behind the 78 degrees please ?
|John Hinkley||08/04/2019 16:07:02|
738 forum posts
Logic? I don't do logic! The first figure was plucked out of thin air and the following ones were calculated to give equally divided spacing between the holes. I could just as easily have chosen a smaller initial angle and had a different layout. So long as the holes in the other plate are offset by one degree, the progression is the same. Try it in a CAD program. That's how I trialled it.
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