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Setting circles laser engraved strip for GEM

ATM beginner DIY equipment mount
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14 replies to this topic

#1 mr.otswons

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Posted 17 November 2019 - 08:18 AM

I have looked and searched for an easy way out but have come short. I want to make setting circles with a vernier scale for my DIY equatorial mount in the making.

But circles as a strip, such as one finds on commercially made mounts, from worse to better quality. I have access to a laser engraver, and think of taking a thin strip of brass or other metal and laser engrave it then cut it out and make it into a ring.

I have found this archived topic on CN

It doesn't say what program, and my coding skills are zero.

 

Also a method mentioned in a topic, from S&T August 1974, A 12 1/2" Newt-Cass by Wilfred J. Sheehan. The method is described using a drill press to make the markings. I do not fully understand how it is done, also due to language skills shortcomings.

 

My goal is to make something resembling a Unitron Model 142 mount or similar, and then align the mount and the scope on all axis as described in https://www.skyandte...your-telescope/

 

Perhaps someone have a vectorised file to share or a simple method to make it in Indesign or Photoshop. I do not know how to operate Illustrator unfortunately.

 

A worry is to be precise when making the strip go full circle and then attach the ends to each other, without any gaps or overlaps. If members think that is nearly impossible and the press drill method is superior, I will appreciate advice on an easier explanation of the method.

 



#2 Xeroid

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Posted 17 November 2019 - 10:20 AM

You may wish to review this web site as it provides several different methods to print circular or linear scales:

 

https://www.blocklay...iming-tape.aspx


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#3 kathyastro

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Posted 17 November 2019 - 10:50 AM

A worry is to be precise when making the strip go full circle and then attach the ends to each other, without any gaps or overlaps. If members think that is nearly impossible and the press drill method is superior, I will appreciate advice on an easier explanation of the method.

That is indeed a problem because of the thickness of the metal strip.  The inner and outer circumference will be different when the strip is bent, requiring part of the metal to stretch or compress.  Calculating the exact correct length of the strip in advance would require some advanced metallurgical knowledge.  (Of course you can determine the approximate length geometrically, but that will not account for the metal's properties when bent.)

 

The practical solution is to work out the correct length empirically.  Bend a strip of the intended metal to the desired curvature, and then cut it to the exact length you need to get the ends to meet perfectly.  You will determine the length by trial and error, so you will need multiple samples.  Once you know the exact length needed, compute the spacing for the markings and do the engraving.


Edited by kathyastro, 17 November 2019 - 10:52 AM.

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#4 mr.otswons

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Posted 17 November 2019 - 10:53 AM

You may wish to review this web site as it provides several different methods to print circular or linear scales:

 

https://www.blocklay...iming-tape.aspx

Thank you! Very good advice!

But I do not see a clock scale. Would be good with a hour minute scale


Edited by mr.otswons, 17 November 2019 - 11:10 AM.

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#5 mr.otswons

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Posted 17 November 2019 - 11:00 AM

The practical solution is to work out the correct length empirically.  Bend a strip of the intended metal to the desired curvature, and then cut it to the exact length you need to get the ends to meet perfectly.  You will determine the length by trial and error, so you will need multiple samples.  Once you know the exact length needed, compute the spacing for the markings and do the engraving.

Definitely agree on empirical, trial and error solution. Thank you,



#6 Oberon

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Posted 17 November 2019 - 12:31 PM

I consider the wrap around strip method to be so difficult as to be practically impossible, and would encourage you to utilise a flat printed (or engraved) plate if at all possible, which can be done very professionally.


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#7 mr.otswons

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Posted 18 November 2019 - 07:03 PM

I consider the wrap around strip method to be so difficult as to be practically impossible, and would encourage you to utilise a flat printed (or engraved) plate if at all possible, which can be done very professionally.

Oberon, I have read several of your topics on your projects, and an advice from such a great maker as you will be heavily weighted in my consideration! Thanks!

And then so many great things have happened when somebody says something is impossible ))))))

I now see the many impractical aspects of wrap around strip idea. What if one takes a very short piece of a tube and cuts scale on that? Wouldn’t it be easier (than wrap around) to achieve some sort of high precision just by taking great care in finding the middle of the ring and then proceed to mark sides of the ring, then half and so on and so on. Marking made by engraving pen or awl directly on the metal step by step.



#8 JohnH

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Posted 18 November 2019 - 07:05 PM

Why not just engrave it on the item in question?



#9 Oberon

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Posted 18 November 2019 - 10:24 PM

Not impossible to do, just impractical, as in extremely prone to error. That said, if you really want to do it, Kathy has probably nailed it.


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#10 JohnH

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Posted 19 November 2019 - 03:36 PM

Not impossible to do, just impractical, as in extremely prone to error. That said, if you really want to do it, Kathy has probably nailed it.

It was done on mine, though the maker was on a skill level par with Byers or Mathis.


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#11 mr.otswons

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Posted 20 November 2019 - 02:20 PM

Thank you all for the input in my thinking process. Now it has come full circle back to Wilfred J. Sheehan article from S&T 1974_08. And here I meet a language problem. My native languages are Russian and Norwegian, and many times technical terms are difficult to grasp. Please help!

He uses a drill-press to mark the circles. It is unclear for me what the tool is in the drill press chuck – a sharp-pointed rod – he writes. Would that be any metal rod? And by rotating it makes the marks? The lower picture on page 118 shows a cutting tool. I do not understand how this works. Does it rotate or just "scrapes" the marks on the circle by downwards motion?

Reading further:

Back on the table, a 1/16" stub drill was used to make indexing holes, cutting through the aluminium and into a steel piece held underneath.

The indexing holes are mentioned earlier as well, but what function do they have?

Next paragraph: To hold the circle-graduating tool, I used part of a circle cutter, usually...

What is the circle-graduating tool?

 

Attaching screenshots of the quoted article:

 

 

Attached Thumbnails

  • S&T p 117 Wilfred J. Sheehan 1974_08.png


#12 mr.otswons

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Posted 20 November 2019 - 02:21 PM

S&T p 118 Wilfred J. Sheehan 1974_08.jpg



#13 mr.otswons

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Posted 20 November 2019 - 02:22 PM

S&T p 119 Wilfred J. Sheehan 1974_08.jpg



#14 BGRE

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Posted 20 November 2019 - 04:17 PM

The sharp tools are probably pieces of high speed steel (HSS) that are typically used in a lathe for turning.

The tool at the bottom of p118 probably moves up and down to scrape a line on the workpiece.

The setup includes a crude form of indexing using a series of holes and a pin. Somewhat like that used in a dividing head.

 

The workpiece is clamped to a bar with a hole and a pin that lines up with one of a series of holes in a usually circular subplate.

By rotating the workpiece so that the hole in the bar aligns with the next hole in the circular subplate the workpiece is rotated through an accurate angle.

 

Google indexing plate and dividing head to get more detail.

 

By circle cutter he means flycutter like those used to cut large diameter holes in thin sheet not the flycutter used to achieve a fine finish in a milling machine.

 https://www.mscdirec...?navid=12106163

in the US these are called trepanning tools or circle cutters.

 

I have one that I can take a picture of if you cant find one on the web.

 

The circle graduating tool is probably the sharp pointed tool that scrapes a line in the workpiece.

 

The tool held in the drill chuck at the top of p118 is a hole cutting fly cutter.


Edited by BGRE, 20 November 2019 - 04:19 PM.

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#15 mr.otswons

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Posted 22 November 2019 - 11:58 AM

The sharp tools are probably pieces of high speed steel (HSS) that are typically used in a lathe for turning.

The tool at the bottom of p118 probably moves up and down to scrape a line on the workpiece.

The setup includes a crude form of indexing using a series of holes and a pin. Somewhat like that used in a dividing head.

 

The workpiece is clamped to a bar with a hole and a pin that lines up with one of a series of holes in a usually circular subplate.

By rotating the workpiece so that the hole in the bar aligns with the next hole in the circular subplate the workpiece is rotated through an accurate angle.

 

Google indexing plate and dividing head to get more detail.

 

By circle cutter he means flycutter like those used to cut large diameter holes in thin sheet not the flycutter used to achieve a fine finish in a milling machine.

 https://www.mscdirec...?navid=12106163

in the US these are called trepanning tools or circle cutters.

 

I have one that I can take a picture of if you cant find one on the web.

 

The circle graduating tool is probably the sharp pointed tool that scrapes a line in the workpiece.

 

The tool held in the drill chuck at the top of p118 is a hole cutting fly cutter.

Thank you so much!

I think I have it now.

The new tool for me is the indexing plate/dividing head. Super cool knew knowledge! Going to read up on this now.

 

I have bought a circle cutter earlier, some topic here on CN about baffles and how to make them out of old CDs with a circle cutter:))

 

Bless the CN forum for generosity of sharing knowledge and experience!




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