A brass indexing attachment for a rotary table I made

[george wilson]

I thought it time to post some actual machining work rather than hand work!! This brass indexing attachment was made for my 6" rotary table.

Believe it or not,I spaced all the holes with a simple Starrett divider with square legs(Fay legs). After marking out the holes,I hand center punched the marks,and drilled each punch mark with a pump drill I also made,including the spade bits for it.

I found that often I could come out nearly right on the mark,with one extra adjustment to get the desired spacings after I had gotten going.

The pump drill is a simple drill which you push down on the handle and start the wheel rotating. Then,it's up and down on the wooden cross bar. The good thing is,you are drilling slowly,and if the drill gets a bit off center,you can tilt the drill and get it back on center perfectly. This must be done before the spade bit gets its corners fully into the hole.

After I got the holes done,I used a small center bit in the drill press to deepen and bevel the edges of the holes.

The knurls seen are the old fashioned microscope type knurls no longer available. I made these knurls too. They were made by running blank knurls horizontally against a rotating tap held in collet chucks in the lathe. The tap does a nice job of hobbing the teeth of the knurl,if all is done correctly,and the knurl rotates freely.

This dividing attachment has developed a beautiful dark golden patina which I only use clean gloves to handle. So far,it is still undisturbed in the finish after decades.

I have included a few pictures of making a knurl. I had made several other pictures,but they are bad,so I need to re do the knurl making process and re present it at another time. My little digital camera has an auto focus that is unreliable. Other than that,I am not a good photographer anyway!

I will advise anyone attempting to make these knurls to use a 3 or 4 flute tap,so at least 1 row of teeth is engaged all the time,to keep the knurl rotating. You also can tilt the knurl about 20 degrees to make a rope type knurl. Too much tilt,and the teeth of the tap start cutting on their back sides,making a mess.

The knurl needs also to be cut hollow pretty close to the diameter of the tap,or it will not work,and you will end up with a mess. That is,the hemispherical groove you cut in the wheel blank needs to match the diameter of the tap reasonably well. If not,the knurl will not turn out properly,and may be ruined.

 

[stupoty]

That looks very nice,

do you harden the knurls for use on brass or are they ok as is?

stuart

 

[george wilson]

I harden them,of course. I use W1 or 01 for them,harden and draw to a medium brown color. They are used on steel too.

 

[george wilson]

To figure out the number of holes for the plate,I had to find a table that gave them for 90:1 ratio instead of the more usual one used in normal index heads.

The fact that I was able to space out these holes with a simple divider should encourage those of you who would like to make index attachments for your own rotary tables. It's been a long time since I made this unit,and I can't recall where I got the needed information ,but it's out there.

 

[Curtis]

That is gorgeous work, George! Also, I seldom see information on how to make "rope knurls" like the one you have pictured here. The only other post on the subject that is on the net (as far as I have been able to determine) is at Frets.com here: http://www.frets.com/HomeShopTech/Projects/RopeKnurl/ropeknurl.html
Great stuff George and thanks for posting it for the rest of us to see.

 

[fishy-steve]

Hi George.
That really is beautiful work.
I'm thinking of making my own dividing plates so that I can machine some gears. Your method of stepping off with a dividers is not one I considered.
Could you explain how you accurately get the correct spacing of the dividers.
I'm thinking, for example, if when setting your dividers for your 43 hole circle you were only .001" out on your dividers you would be .043" out on your last hole.
How do you do it??

Thanks,
Steve.

 

[Ray C]

Wow. Very nice, George.

Wish I could that...


Ray

 

[george wilson]

Early Dutch clock makers had to rely on simple dividers to space their gear teeth. They were able to make very accurate gears by spacing in a large circle which the actual gear was placed in the dead center of. after the spacing was done,they used large dividers to swing the arcs of the division marks down to the gear,marking the teeth. By the 18th. C.,factory made dividing engines were available for clock and watch makers.

The clock and watch industry formed the basis for building the machine making industry we had later on. It was a very important beginning where many mechanical principles were figured out,such as how to divide larger gear teeth for machines,milling,precision lathe work,etc..

As for me,I just stepped out the divisions right on the brass. fishy-steve,I soon got able to make a very small adjustment to the divider's wheel to do the next smaller circle. I'd get the last scratch right into the scratch where I started. Not that hard,really,after a bit of practice. Beyond that,the divisions were put through a 90:1 reduction in the rotary table,providing exceeding accurate indexing.But,I can assure you,the spacing on the brass wheel itself was accurate to use right off the plate for just about anything except possibly spacing of astronomical instruments. Have you seen the early Ramsden spacing device in the Smithsonian? A large brass wheel about 3 feet dia.,or more. It has a small worm wheel with knife edge threads for fine adjustment on the o.d. of the wheel. The instrument being made was secured to the center of this large wheel.

 

[FOMOGO]

That is very impressive work George. By the way, Does Dennis still live next door? Mike

 

[RandyM]

Thanks George. Very nice work indeed.