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Making Degree Graduations

Posted: Fri Jul 29, 2011 4:01 pm
by seal killer
All--

I would like to create about 20 one degree graduation marks on the adapter plate in my telescope pier project. They are not a requirement, but it would be nice to have them during setup of the telescope. They would be located on a 5" diameter (approximate) circle.

I don't really have a clue how to do it. But, I am thinking of mounting the adapter plate on the rotary table and using something in the spindle to create a mark about 0.125" long by moving the table that distance. The next mark would be created by cranking the table 1* and repeating the procedure. The marks would have to be deep enough to still show after the adapter plate is painted.

How might this actually be done?

--Bill

Re: Making Degree Graduations

Posted: Fri Jul 29, 2011 4:37 pm
by BadDog
I think you've basically got it. A broken drill bit or end mill could be ground to provide the cutter. The business end (looking down the bit axis) would look like a triangle with one shorter side, and maybe a bit of rake back toward the short side. The point opposite the short side is the cutting edge. Lock the spindle so it can't rotate (may have to rig something, doesn't need to be perfect or terribly robust) with the point oriented roughly "square" (or "normal" or whatever you want to call it) to the edge you want to score. The in-feed should be radial to the rotab rotation axis. With the plate centered on the rotab axis, make the mark by "stroking" the quill. Set a stop so you get repeat length of stroke, and feed in till sufficient depth achieved. In feed will likely start on the order of a few thou per stroke and see where it takes you. As you get deeper, you may need to reduce in-feed per stroke. Rotate and repeat till done. Extra points for making every 5* multiple mark ~10-20% longer to easily differentiate. More points still for a vernier implementation. :D

Re: Making Degree Graduations

Posted: Fri Jul 29, 2011 5:34 pm
by wsippola
A slitting saw on an arbor makes very nice graduations, and I expect would be much quicker than a single lip engraving type cutter. It's also nice to make every 5 deg mark somewhat longer, and the 10 deg marks longer yet.

Wayne

Re: Making Degree Graduations

Posted: Fri Jul 29, 2011 6:26 pm
by Jose Rivera
The ideal tool would be this http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 2426wt_849

I just bought 10 for little change.
They come on different included angle points.

This is much better that a slitting saw, but a very thin and small diameter should do fine.
Maybe more durable.
Those styluses require high RPMs.

Re: Making Degree Graduations

Posted: Fri Jul 29, 2011 7:24 pm
by Lew Hartswick
I did that for a project that the kids do school. I just took a 1/8" carbide burr that had been
"used up" and ground a point on it, put it in the spindle and, in our case, traversed the
table to make the scale. It was just a linear scale. So the rotab would do for the arc.
...lew...

Re: Making Degree Graduations

Posted: Fri Jul 29, 2011 10:16 pm
by mechanicalmagic
Bill,
You can use a fly cutter in the horizontal axis of your mill. Grind a cutter with a ~90* included angle on the periphery. Too narrow a groove will try to suck up paint.

Dave J.

Re: Making Degree Graduations

Posted: Fri Jul 29, 2011 10:18 pm
by dly31
Some people just use a lathe threading or similar Vee shaped tool to do the scribing.

Re: Making Degree Graduations

Posted: Fri Jul 29, 2011 10:38 pm
by seal killer
Russ and Wayne and Jose and Lew and Dave and dly31 and All--

Lots of ideas. Thanks!

I am going to experiment on some scrap.

--Bill

Re: Making Degree Graduations

Posted: Sat Jul 30, 2011 5:54 am
by bjmh46
Image

Image

I'm with Jose. These are done with a ho-made engraving cutter--D-cross section, 30 degree included angle. Fine for aluminum--little delicate for steel. I like the "crisp" end of the grad line you get with a cutter like this, as opposed to the "tail-out" termination you get with a slitter or fly cutter. But, there are many ways to do do this and it's a matter of personal preference and expedience. Good luck with your grads!

Regards

Bob

Re: Making Degree Graduations

Posted: Sat Jul 30, 2011 6:03 am
by seal killer
Bob--

Beautiful!

--Bill

Re: Making Degree Graduations

Posted: Sat Jul 30, 2011 6:06 am
by seal killer
Jose--

How fast do you have to turn those styluses?

--Bill

Re: Making Degree Graduations

Posted: Sat Jul 30, 2011 3:06 pm
by Harold_V
seal killer wrote:Jose--

How fast do you have to turn those styluses?

--Bill
Almost impossible to drive them too fast---considering they have an almost zero diameter. 20,000 rpm wouldn't be unreasonable, and in aluminum you could justify more than 50,000.

Harold