Shatterproof Tempered Glass vs Lexan Enclosure Window

I recently completed a PM833 conversion with an enclosure designed to contain the chips. See Another PM-833TV Conversion - CNC Mill Conversions and Builds - Dr. D-Flo ( for complete build info. The enclosure works well, but I am contemplating upgrading the shower curtain closure for a shatterproof glass or Lexan window. I would love to hear feedback on the following:

  1. Do I really need protection from flying objects? Many articles I read suggest the importance of a screen of some sort (Lexan or glass) to protect the operator from something flying out of the machine. With a spindle speed of 3200 RPM, is this really necessary. I see most professional CNC machines offer protection of some sort but the manual Bridgeport’s of the world do not. What are your thoughts?

  2. What is the best material for the window? Shatterproof tempered glass or Lexan. Lexan surely offers more protection, but I assume that after wiping aluminum chips off of it will scratch quite a bit. I think there is a scratch resistant version, but wouldn’t it scratch after a while as well? I think you can also get ballistic glass, but it may be crazy expensive. I welcome your thoughts.

Thanks… Richard

One of the top safety concerns is the part flying out of the vise/fixture. With manual machining, the feed rate is more conservative and the operator can see how the part responds (vibrates, shifts, etc.) when just starting a cut. With CNC, the cutting tool zips across the top of the part, which gives the operator very little time to react and the part flying if not properly secured. This danger is amplified when using a large, powerful VMC.

I ran my PM-833TV without an enclosure for about 2 years without incident. However, I always had my feed override set to a low value at the start of an operation just to be sure everything looked good.

I just finished building my enclosure with Lexan/polycarbonate windows, and while safety glass will be clearer for longer. It is harder to mount and usually more expensive to procure. It is very easy to order polycarbonate from SendCutSend with some through holes for mounting. Also, it will conform to uneven surfaces without shattering. I will have to report back how well the windows hold up to scratches.

Nice job on the enclosure & thanks for the feedback. I have now run a total of about a dozen parts and coming to same conclusion that I would feel more comfortable with something between me and the possible flying parts. I will post an image of my improved enclosure shortly.

Thanks for your thoughts… Richard