View Full Version : Grind plastic?

03-29-2005, 12:58 AM
Been looking to get a used surface grinder at work for a while now and thought of a potential use. I need to make adhesives testing panels from various plastics and don't have an extruder. I can buy most plastics already smooth enough for my needs but some things like nylon have a rough machined surface. So far I've been doing this with a table mount belt sander and light pressure but it's hard to get a flat surface. Do you guys suppose I could setup a surface grinder and do this with light cuts? If so any recommended wheels?

-Christian D. Sokolowski

03-29-2005, 04:18 AM
If a dremel has taught me anything, it's taught me that grinding plastic turns good stones into good plastic covered blobs http://bbs.homeshopmachinist.net//smile.gif

I spent a number of years working in a vacuumforming plant and the various ways we made parts smooth again were :

Flame polishing. (propane torch and a light touch)

Big smelly rag dripping with MEK or other scary solvent. I don't think that would work for nylon and its not pleasant or even remotely healthy.

Plunge router with a bearing guide and a pattern that either clamped on the part or a vacuum system holding the part down into the pattern.

A scary as heck band saw that was modified to lay on its side and had a custon table made that could be raised or lowered to set the cut height. Imagine pushing a part towards 24" of exposed blade one inch off the table.

If your test won't be affected by it, why can't you use a smooth piece of metal that has been heated up to the forming temp and then press the rough side of the plastic down onto the metal and cool both?

03-29-2005, 05:30 PM
One word for making plastic flat, flycutter. A single bit of HSS with the right geometry (sharp like woodworking tools) will give a good finish down to .001 without the mess of other types of finishing. There may be better methods but that's what I always use.

03-29-2005, 07:37 PM
Thanks guys,

Actually I tried the flame trick but I'm not that skilled. Second I tried the heated plate trick and a press and it didn't work much better. Third I have used a flycutter with decent results, a face cutter worked even better. I actually found that very high speed and slow feed worked the best for that but I was still left with swirled marks that are deeper than my adhesive coating thickness. I got very good results with the belt sander but ruined some panels by holding them with either too much pressure or for too long.

We've been talking about buying a surface grinder to add to our shop anyway so the other day I took a panel to a fine wheel on my bench grinder and got a surprisingly smooth surface, the key was to move the panel fast with little pressure but freehand just won't cut it in this application. I need a smooth as possible surface. My plan is to do the rough cutting on the mill with the facing cutter and then just skim the surface with a fine wheel and mist coolant on a surface grinder. I'd like to get one with power transverse and possibly add a DC gearmotor to get the table to move faster if need be. I know that fine sandpaper works because I've done it on the belt sander so I'm thinking a surface grinder would allow me to have better control over the panels thickness which is important in this application.

We will also be using this machine to lightly polish various metals for adhesives testing as well as for general use in our machine shop so it's not a big deal if I can't get it to work. This is sort of a last ditch effort before I invest big money into an injection molder or extruder and slot die.

My company is a small family owned adhesives and coating company for which I do many jobs including all the machine work. The machine shop is sort of my little bonus as I have 24 hour access to any machine and even have my personal CNC Boss 5 installed there. My boss is crazy like a fox and knows all too well that buying me "toys" keeps me happy and very productive. http://bbs.homeshopmachinist.net//smile.gif

Anyway tommorrow I am going shopping for a used grinder, I have a budget of $1500, any suggestions?

-Christian D. Sokolowski

C. Tate
03-29-2005, 08:53 PM
It is possible to grind plastic. I cannot reccomend wheel but Norton could. I have not seen parts off of surface grinder but have seen parts off of centerless grinder. If you can do it centerless you can do it surface. Wheel is the key.

03-30-2005, 06:11 PM
I've got a new toy! Picked up a really nice hydraulic Brown & Sharpe 618 Micromaster for $1500 at a local machinery reseller. Now all I need to do is make room for it in the shop and wire another 3 phase circuit.

-Christian D. Sokolowski