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More work on the tool holder.
Hi Guys,
Sorry for taking such a long time to get back to doing some more work on the Brooks TCG. Apart from other things getting in the way, i've not felt up to it.
It was way back in November when I made the base plate for the tool holder. Since then I've been thinking about how the tool holder itself will fasten to the base and how to adjust and control the angle that the tool will be set at.
One criteria is the ability to accurately repeat any angular setting. In order to achieve this I've decided to try and make a worm and wheel type of assembly, a bit like a miniature rotary table. The drawing below is an attempt to illustrate what I want to do.
Attachment 384228
The black outline is the proposed tool holder mounting plate. The red line is the partially toothed disc upon which the actual tool holder block sits. The green lines are the tool holder block and the tooth depth I want to achieve, which works out at 3 mm for an M8 X 1.25 pitch thread.
The drawing, blue lines, shows two views of the threaded rod and its mounting blocks, and how it would be placed. Since there is very little depth in the screw mounting bearing blocks, I've shown a view, to the left, using M4 threaded studs that can be soldered into place and have a nut used on the underside to secure them.
I am using a piece of 70 mm diameter, 10 mm thick hard aluminium plate for the toothed disc. The disc will be mounted on a pair of 696ZZ ball race bearings, which are 15 mm diameter. Because of the disc thickness, I'm using two bearings pressed together.
Attachment 384234 Attachment 384235
I started with a 72 mm square piece of aluminium plate. I found the centre and marked it with a centre punch. After which I drilled with a 4 mm drill followed by a 14.5 mm blacksmiths drill. Finally reaming out to 15 mm - 2 thou. The picture shows the two bearings that I am using. they are NTK 696ZZ ones made in Taiwan. 10 for £3 inc delivery from Banggood.
The second picture shows the bearings dropped in place. They are a good finger press in place and I had to use a hot air gun to allow them to fall out.
Attachment 384232 Attachment 384233
I then turned up a steel mandrel on the lathe, drilled it to take an M6 cap screw, turning it down so that the aluminium piece was a good fit, before fastening it ready for turning to 70 mm diameter.
Attachment 384231 Attachment 384230 Attachment 384229
These three pictures are after turning the square piece into a disc and refitting the bearings.
This is as far as I've got for now ! I need to make a fixture to support the disc on the lathe whilst hobbing the teeth into it. I've calculated that I need a minimum 35 mm length of teeth to allow a +- 15 degrees of adjustment.
I'll come back when I've made the fixture to cut the teeth.
Thanks Guys for your support.
Thoughts on a Worm & Wheel.
Hi Michael,
Quote:
Originally Posted by
Michael G
Thanks
Quote:
While a worm can be cut with a tap as you are proposing (I've seen pictures of it done with telescope drives), the teeth will not be all that big and at a 60 degree pressure angle, I would be concerned that there would be a tendency for the teeth to try to cam out of the slots.
Entirely your call, but there are a couple of ways of making wormgears that I think will do the the job better. Let me know if you want a better explanation.
Michael
Thanks for your post ! I am all ears. I've never cut any gears. I've either purchased them or salvaged gears from other things that used them. So this would be my first attempt to actually make any. In that context I'll take any help or advice that I can get.:)
First let me try and describe my idea. Since I only want to cut teeth on a segment of the disc, I was thinking about using an M8 X 1.25 pitch tap as a hob, using the lathe spindle to turn the tap and mounting the disc on the cross slide. Marking the disc with the start and finish points for the length of teeth that I want to cut. Then using the cross slide to adjust the depth of cut. If necessary stopping and going back to the beginning to cut the teeth deeper. The use of an M8 tap was simply because I could then use a length of threaded rod as the worm. Also because the disc will have very little loading applied to it, it shouldn't take much force to turn it.
Thanks in advance for your kind offer.
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Another sneaky way to make partial worm gear
See attached file. Shows an interesting variation on the "use a tap to make a worm gear" idea. Possible to cut the curved recess by using a milling machine or a form tool on lathe..