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Old 22nd Nov 2017, 9:03 pm   #2
David G4EBT
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Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 5,737
Default Re: Cutting (router) a circular flashover guard for me?

I'm not volunteering my services, but I hope the following observations might help a little.

First Al, you're right in thinking that a router would be the neatest way of cutting the two circles. It would require a circle cutting jig - an accessory which most router users would make. I don't have such a jig, nor the time to make one, but someone on the forum may well have one and prepared to undertake the project. Here's a typical example, which illustrates what you're wanting to do:

https://www.bing.com/images/search?v...=16&ajaxhist=0

Here is a two-part video on how to make a DIY circle cutting jig, for anyone who might be so minded:

https://www.bing.com/videos/search?q...er&Form=VQFRVP

https://www.bing.com/videos/search?q...92&FORM=VRDGAR

As to material, I'd suggest that FR4 fibreglass sheet would be a good choice - basically, it's the same material as the substrate on fibreglass PCBs. ('FR' stands for 'flame retardant').

To quote Wikipedia (instant erudition for the hard of thinking!):

FR-4 glass epoxy is a popular and versatile high-pressure thermoset plastic laminate grade with good strength to weight ratios. With near zero water absorption, FR-4 is most commonly used as an electrical insulator possessing considerable mechanical strength. The material is known to retain its high mechanical values and electrical insulating qualities in both dry and humid conditions. These attributes, along with good fabrication characteristics, lend utility to this grade for a wide variety of electrical and mechanical applications.

Source: https://en.wikipedia.org/wiki/FR-4

You don't mention the thickness of material you wish to have - I guess you may feel 'the thicker the better, but obviously the thicker you use, the more expensive it will be. Ideally, a piece 12" square (30cms) would be the optimum, but suppliers seem to supply A3, A4 and A5 sizes or other oblong sizes. Here are a few examples. The first is 2.4mm thick (as with PCBs):

FR4 fibreglass sheet 2.4mm x 16” (40cms) x 12” (30cms). £17.99 plus £3.99 P&P:

https://www.ebay.co.uk/itm/2-4mm-16-...-/292338986441

This source can supply 3mm/5mm/10mm thick and you’d need an A3 sheet, which - if 5mm thick - would be £22.00 plus £3.00 del. (10mm thick would be £43.00):

https://www.ebay.co.uk/itm/Epoxy-Gla...sUmapKsAxiOkvw

When you say 'it needs to be in two halves' just for clarification, do you mean as shown in the sketch below? If so, I just wondered why, and how it would be mounted.

As I say, I'm unable to help, but I hope these observations might move things along a little for you or anyone who might wish to undertake the task.

Every good wish with the project.
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