How can I make adjustable circle attachment for pantograph

Danny D · Apr 21, 2020

I have a Heath pattern tracing pantograph torch that suites my needs very well. While it is easy for me to make a circle sheet metal pattern for the magnetic stylus to follow it will only cut one size circle. I would like to figure out an infinitely adjustable circle cutting attachment that would let me use the variable speed and stylus feed as it does when using a pattern. I envision something like an adjustable compass or a trammel to guide the arm instead of a pattern but I can’t figure out the feed. I am well acquainted with CNC torches and understand how they can cut infinite circles with ease but I don’t have one and I don’t want to wait a few days to pick up my parts.
Ever seen anything like this?
Thanks, Danny

Illinoyance · Apr 22, 2020

With the Heath you will need individual templates for the circles.

Danny D · Apr 22, 2020

Yes, that’s what I’m doing now. I could build an attachment that would allow the torch to swing any circle but how to make it power feed is the challenge.

dana gear · Apr 22, 2020

Illinoyance said:
With the Heath you will need individual templates for the circles.

Many years back we ran a Heath for basic circles with a plasma machine torch, We had a bunch of circle patterns and used a quick change adapter to hold the disc, swap outs only took about a minute. Down the road you may want to look into a CNC plasma cutting table.
In the time it took us to cut 6-12" disc on the Heath we could blow out a 48"x120" sheet full of nested 12"circles.

DDoug · Apr 23, 2020

dana gear said:
Many years back we ran a Heath for basic circles with a plasma machine torch, We had a bunch of circle patterns and used a quick change adapter to hold the disc, swap outs only took about a minute. Down the road you may want to look into a CNC plasma cutting table.
In the time it took us to cut 6-12" disc on the Heath we could blow out a 48"x120" sheet full of nested 12"circles.

Same here, and throw in an electric eye machine as well.

Then I cobbled together someone else's project machine, using mach3 and steppers, and never looked back.

Lantraxco · Apr 30, 2020

Does the Heath have a collet to hold the magnet shafts? Build a blank shaft with a small pulley for a flat timing belt, a larger pulley fixed at your center point, and an adjustable takeup idler on the slack side. An adjustable rod or frame on a bearing to set the radius. Probably have to buy several different length belts to match different ranges, but they're cheap. Don't use chain, makes the torch stutter as it moves, don't ask how I know, lol.

DDoug · Apr 30, 2020

Lantraxco said:
Does the Heath have a collet to hold the magnet shafts? Build a blank shaft with a small pulley for a flat timing belt, a larger pulley fixed at your center point, and an adjustable takeup idler on the slack side. An adjustable rod or frame on a bearing to set the radius. Probably have to buy several different length belts to match different ranges, but they're cheap. Don't use chain, makes the torch stutter as it moves, don't ask how I know, lol.

Unistrut for the slide adjustable length, the rubber belt have a 3rd pulley
as an adjustable idler, much like a potato conveyor for loading trucks.
These extend out, idler moves to take up or pay out slack.

dana gear · May 1, 2020

One consideration is how accurate plus/minus diameter do your circles need to be.
It may be hard to hold circular dimension if that's a concern.

DDoug · May 4, 2020

dana gear said:
One consideration is how accurate plus/minus diameter do your circles need to be.
It may be hard to hold circular dimension if that's a concern.

Using which style of cutter ?

dana gear · May 4, 2020

digger doug said:
Using which style of cutter ?

Just pointing out that a simple adjustable apprentice for cutting different disc sizes on a Heath pattern cutter would probably be hard if not impossible to hold very close tolerance, if a very tight plus or minus is not a concern then no problem and power on.
Years back we used a pattern cutter for several different size discs that were quick change. Along with early high definition plasma we held a very tight +/- of finished diameter.

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