Cutting glass reinforced plastic - ideas?

[TinyShop]

Hi all - I need to remove some thin tabs, cut out a small section of the thin (~3mm) floor and grind/sand down some narrow elevated ridges (the latter left over from the mold) of an accessory that is constructed of glass reinforced plastic. I've read that this material is quite difficult to machine (dulls cutting surfaces rapidly and is very dusty) but since I have so little to remove I'm thinking I can have at with a MultiMaster (with maybe a regular cutting blade(s) followed by the sanding head w/dust extraction). The cutting needs to occur in a narrow recessed area about 5 inches long, 2 inches wide and 1 inch deep which is why the MM seems like it would work the best. I'll turn the speed way down (high RPMs/oscillations are apparently bad in this material) when cutting and then when sanding too. I'll sand with the MM since thats the only delta-head sander I have and I need to get in some tight areas.

Does this sound like a wise approach? Or would an angle grinder perhaps be better? Obviously, if this accessory was made of steel that would be the way to go. But an angle grinder in this material seems like trouble given the high RPMs and what seems like what would be a tendency to melt the resin binder (another bad idea I've read).

This work takes place on the back (unseen area) of the accessory so it doesn't have to be pretty though I'll take care to make it look somewhat presentable.

I'd appreciate anyone's thoughts.

 

[Klemm]

[member=64030]TinyShop[/member]  - have you considered a die grinder with a tapered carbide cutter (cone comes to a point)?
You can get in tiny crevices and likely have less chatter than a Multitool cutting out ribs and moldflash.
Figure out a way to hold the workpiece with clamping so you have two hands to control and manipulate the die-grinder. Of course, full face shield and nose-mouth respirator.

Maybe Cheese here on the FOG will chime in - this project is right up his alley. [wink]
Let us know what you ended up using and how it worked out.

Hans

 

[Cheese]

A photo would help a lot as you’re talking about tabs which I would assume are a subset of molding and you’re also talking about a floor of some sort?

Without a photo, my initial thought would be to use a diagonal cutter on the tabs to reduce their height by 90% and to then use as Hans mentioned a small die grinder to further smooth the surface.

A die grinder using a small 1-2” disc can be throttled judiciously to remove the remaining “flash” while still producing a smooth surface.

Also of importance, reading between the lines I feel like this isn’t a one time item deal but a several item deal which may change the overall solution.

Also to be noted is that small name brand air operated die grinders are cheap when compared to just about anything that has Festool emblazoned on it.

As noted before, a photo or two would be a huge help.  [smile]

 

[TinyShop]

Thanks for the all the advice! I ended up going with the MM fitted with a fresh Bosch "All Purpose" blade. Surprisingly, I had no problems at all cutting or milling the material. The thickest sections that I removed were only 2mm or 3mm thick and the blade easily powered right through it. I cleaned up my cuts using the cutting edge of the blade to "sand" down any rough spots. Couldn't have been easier. The material also sanded easily too. Obviously stronger than regular plastic but not inordinately so.

I'll post (hopefully tomorrow) the results of this small project under a separate subject line called "Karcher Sys-Dock to Starmix i-Pulse Hack". Stay tuned!   

 

[Klemm]

[member=64030]TinyShop[/member]  - thank you for the MISSION ACCOMPLISHED report!

Hans

 

[TinyShop]

After some fits and starts I was able to successfully post about the reason behind needing to cut glass reinforced plastic. Anyone interested can check out the related post here.

 

[Michael Kellough]

That Karcher thing? From the photos it doesn’t look glass reinforced, just polypropylene.

 

[TinyShop]

That Karcher thing? From the photos it doesn’t look glass reinforced, just polypropylene.

It looks to me to be glass reinforced but the percentage of glass also appears to be very low. If I have a chance I'll check the mold markings and see what they divulge.

 

[AlexThePalex]

Looks like just plain plastic, no glass in there. How did you get the idea it has?

 

[TinyShop]

Up close is looks just like all the high-strength fittings on my collection of Ortlieb panniers, all of which are glass reinforced and strong as H E double L.

 

[Svar]

When you first posted the question I thought you are talking about something like fiberglass shower pan, etc. Those are tough. The thing you posted later is technically glass reinforced (such as power tool motor housings, etc.) but much softer and easy to cut. You could have done it with a hand chisel.