Machinable Non Compressible Insultator

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Robert LaLonde

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I've decided I need to make some electrical tool height setters for my machines with a fairly small foot print. I've figure out my design so they will have a lot of over travel and good repeatability, but I am wondering about the anvil or touch surface. The analog indicator type I am using now seem to have a steel surface, but they are softer than the tools and they will ding fairly easily if you make a mistake. Because I do a lot of flood machining I was thinking stainless might be the ticket. 304 for the body, and 303 or 416L for the anvil with an acetal insulator. A harder machinable insulator might be better, but I am not sure what.

Definitely NOT something like HDPE since its compressible, and spring pressure over time might cause it to extrude and drift. I don't really have room for an off material setter to to be used all the time. Adding soft buttons and macros to semi automate the tool height set is pretty easy for my controls. It would improve my machine times, and reduce my necessity to deburr between tool changes more easily creating consistent parts.
 
It's not clear to me what the part looks like, but lexan is tough and has very good insulating qualities.
 
Polycarbonate might be a good choice, I'll have to research it.

Cylinder inside a cylinder. Doesn't matter. If it works I'll write it up. If it doesn't work out I'll whine real loud about it.
 
Anodized aluminum is an electrical insulator.

David
 
I use phenolic CE grade canvas sheet, but it also comes in glass filled versions called G10 both in rod and sheet. It is very dense and not pliable, the CE is for electrical, I make control boards with it. I have some 1/4" sheet remnants of the canvas CE grade if you want a piece to play with. Send me your address in a PM and I will a ship a piece in an envelope, otherwise some G10 is even denser and is available online.
 
It's not clear to me what the part looks like, but lexan is tough and has very good insulating qualities.

Seems that polycarbonate can cold flow like many other plastics over time. Research research research. LOL. Here is a rough draft of the idea. Shorts to frame ground when a tool touches it. Can be made with a huge safety over travel. A typical indicator type height setter only has 0.1 to 0.2 over travel usually.

I'm going to give phenolic a shot. If that doesn't cut it then Macor may be next. Phenolic is cheap though and Macor is expensive.

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Typically simple probes and electronic height setters are made with a ring of six gold plated round beads, and the core is an insulator that holds three gold plates pins in a star configuration that short between the gold balls in pairs. Any movement of the probe or table attached to the core breaks the contact. Its a better design than mine because it fails safe. ie: If it fails the circuit is broken and the machine thinks its already touching so it doesn't move. If mine fails it will drive the cutter into the height setter. If I have a broken circuit somewhere with this simpler design the machine won't know. The extra over travel will give me time to hit the e-stop or the feedhold though.

The piston will likely get threaded on top and a table will be mounted to reduce coolant and chip contamination.

If you look at the images you will see a plug that holds it all together. During machining a spacer is used instead of a spring to hold the piston firmly against the insulator so the end of the piton (or the table) can be machined flat relative to the base of the setter.
 
McMaster Carr sells machinable ceramic
 
McMaster Carr sells machinable ceramic

YES THEY DO! $54 for a 3/4" rod 3" long is a bit much though. I use phenolic handles on lead casting molds that are about that size for a little over a buck. I'm going to give phenolic a try. Another member here said they would send me a piece of a slightly different phenolic than the handles I use too.
 
Is phenolic resistant to liquids like coolant and oils?

Its used for making gears, bushing, and rollers so it should be able to handle basic oils. I guess I'll find out. Can't speak for the SC520 with distilled water for my flood coolant, but I can drop Master Chemical an email and find out. They are usually pretty responsive. The thing is if more than cursory crap gets in a height setter it has to be taken apart, cleaned, and readjusted anyway as it will gum up.

These are not to be permanently mounted for fully automated tool changes. In fact if I was setup for fully automated tool changes I would not need them at all. Just enter all the tool heights in the tool table.
 
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