Thread: K & T site glass

I want to change the site glass in my mills. I have some .060 Lexan which I think JohnO said to use.

Whats the best way to cut this stuff I haven't tried yet I figured it would crack easy.

Paul

What do you have to use? Hole saw, hack saw, bandsaw, mill and trepanning tool? Lexan is nice to work with compared to acrylic or plexiglass, it cuts, machines and drills nice, I wouldn't worry too much about it cracking.

I draw the shape on the Lexan, rough cut it out on a vertical bandsaw and use the belt sander to finish it. It works very easily, and IME, it doesn't easily fracture, or chip. Made quite a few sight glasses out of Lexan.
Harry

Clamped between two pieces of hardwood (one in chuck, one shoved on by tailstock) and turned to size in lathe. Eight years, no problems in 36" Ohio shaper.

http://img.photobucket.com/albums/v337/johnoder/Ohio Shaper/DCP_0654.jpg

http://img.photobucket.com/albums/v337/johnoder/Ohio Shaper/DCP_0654.jpg


Same o same o

John - please re-do your link. I get the dreaded "this item has been moved or deleted" message when I click on it.

Good example of what PM (or Photo Bucket) does to links these days. Here is the IMG version

Thanks for the help, I may try all of them.

Paul

Old Iron,

If I had to describe it, some plastic items machine more like rubber in that they are prone to either bend or melt, and some items machine more like glass where they tend to just break, Lexan tends to be more of a "gooey" type of plastic, so when it heats up it is more flexible than crackable, if that makes sense.

Machined a lot of plastic in grad school for lab stuff.

Picked up a few tricks.
Lubricate with vegetable oil. Most plastics dont react to it. Mineral oils are hit and miss.
Run your tools slow enough you dont melt anything and keep the bits oiled.
Plastic sticking to the tool generates a lot of heat and everything goes south fast.

Drills should be re ground to have the leading edge closer to vertical. You want the drill bit to scrape, rather than dig in.
"Rigid" plastics like Lexan tend to be drawn into the bit, then snap away. Thats one of the ways you get tear out around holes.
Sacrificial blocks above and below the part are another good way to deal with this.

Friction chucks, like what Johnoder described work quite well.

Clamping parts between support blocks of wood when milling or turning keeps them from flexing and reduces the chances of scaring the surface.

Recently replaced a broken sight glass on my Schaublin lathe. I used the plastic from a trashed dial indicator which machined like polycarbonate. I used a good quality double stick tape to adhere it to a piece of aluminum held in a three jaw chuck. Worked great!