[kstrauss]

I suppose this is not strictly a Tormach question but I *am* using a PCNC and I know that some of you deal with plastics so...

I'm making some parts of 3/8" thick PVC sheets. One part requires short grooves, 1/8" wide and 0.10 deep, near the middle of the outline. Cutting the grooves is no problem but there is a short "burr" of stringy PVC at the edges that seems almost impossible to clean completely. Varying feeds and speeds helps a little. Very sharp cutters help but not enough. I'm currently cutting dry with an air blast to clear chips. Would coolant help? What do others do to deburr stringy plastics?

[mactec54]

kstrauss

Yes you should be using coolant,put a light chamfer on the edges this will clean up the edges

[SCzEngrgGroup]

For "stringy" plastics, use a straight-flute cutter. A helical tool will create burrs and strings.

Regards,
Ray L.

[mountaindew]

Most my experience is with acrylic in various grades and types. Some cast acrylic by certain brands machine excellent and you end up with almost a clear polished finish.
Other types like extruded machine differently and vary type and brand. The point is there are many grades, formulas and brands of plastics of each type be it acrylic, pvc, uhmw or whatever your working with.
In my experience they can all machine differently depending on any one or all of those factors. Even the age of the material and sun exposure will change the material causing cross linking and other problems.

Experimenting like your doing is about only way to find a sweet spot for your tools at hand.
My only pointers would be,
Anything you can do to keep the cutter cool and free of swarf will help as Mac54 noted, coolant, air or both.
I have found the more rigid you can hold the material the better the finish and results no matter what grade of plastic.
Spanned in a vise and held under compression also causes problems I have noticed.
My best results comes from screws holding it to a flat surface as tight as possible without damage " hard to do this even"
If I see a little spring in the material and how its held it shows in the milling process also.

I have some pvc sheet around here and will run a few test parts for fun to see what happens.
I think its a expanded pvc sheet and could have different machining qualities but I might get some insight anyway. "might be what you using also"

Let you know what I see
md

[tbaker2500]

I run into this with air and flood coolant. While the amount of swarf that is stuck to the part can be greater cutting dry, it doesn't go away with even extreme amounts of coolant. My guess is there is not a single magic bullet, but like many things the cut needs to be optimized, and may never be perfect. I don't have much experience with straight flute cutters like Ray suggested, that may be worth trying.

[SCzEngrgGroup]

For cutting soft plastics (UHMW, Delrin, ,etc.) I use good quality single-flute carbide router bits. They make no strings, and leave no "fuzz" - Just nice, clean cuts.

Regards,
Ray L.

[Steve Seebold]

I have done a lot of plastic machining. I use an end mill with a RIGHT HAND CUT, LEFT HAND SPIRAL and I don't get the burrs you're talking about.

The end mills I use are made by Quinco. The're kind of hard to find, but the work really well.

[bhurts]

Soft plastics leave fuzz at times no matter what you do. Get a deburring tool. It will be your best friend with soft plastics. It will clean the fuzz off almost effortlessly.

Ben

[kstrauss]

Do you mean Quinco Tool Products? I found a catalogue from 2009 (!) on the net that lists their website as quinco.com is under construction which appears to now be defunct. Are you suggesting what is sometimes called a "downcut" bit which is often used in a router to prevent top tearout when cutting wood?

[Steve Seebold]

Do you mean Quinco Tool Products? I found a catalogue from 2009 (!) on the net that lists their website as quinco.com is under construction which appears to now be defunct. Are you suggesting what is sometimes called a "downcut" bit which is often used in a router to prevent top tearout when cutting wood?

They could be called a "downcut" end mill. I used them a lot to cut delrin and abs plastic. They actually push the burr down. You need to use HSS though. Carbide is just not sharp enough to cut soft plastics, Carbide will just push it out of the way.

[mountaindew]

Moving over to router bit style tools you have a bunch of choices imho
Spiral cut bits "look like end mills " their terminology!
Spiral cutters from company like white side make them in upcut, downcut, chipbreak, flush trim, left hand, roughing, 2 flute, slow spiral, up/down compression cutters, zero flute spirals
All of these are made for plastics and laminates "and more" I use a few of these types on my tormach all the time.
As steve mentioned you can get downcut and try it or maybe a UPcompression would have same result with better chip removal.
Even cleaning tool bits with alcohol helps me get better results. I might take some experimenting.

md

As a foot note
be real careful using coolants and plastics like acrylic.
As of right now I can say the coolant tormach sells will damage SOME types of acrylic and cause crazing and cracking.
I recently started using it and noticed cracking in some of my newly machined parts and in the plastic fixture plates I use to hold material in vise.
Real easy to see, I have 2 sets of fixture plates to hold material that I made a couple months ago. one plate used with coolant has cracks and crazing and the other does not.
Both plates were made at same time from same material so no difference in material or they were made.
Kind of double blind control test by accident.

[kstrauss]

Has anyone tried the special bits from Precise Bits ( Precision Carbide End-mills ) that are claimed to be superior for plastics and composits?

[nitewatchman]

Soft plastics leave fuzz at times no matter what you do. Get a deburring tool. It will be your best friend with soft plastics. It will clean the fuzz off almost effortlessly.

Ben

I use a sharp Cabinet Scraper to remove the burr/fuzz from plastics. Using a scraper with a sharp turned burr on the edge I find it is easier to either deburr or chamfer than using a deburring tool. Only exception is for holes, a deburring tool works best here.

Buy 3pc Straight Scraper Set at Woodcraft.com

nitewatchman

[GLCarlson]

"O" flute geometry cutters appear to be a good way to go.
Onsrud Solid Carbide Spiral O-Flute Router Bits

Think n Tinker has microversions. Recent newsletter from them mentioned this geometry, which was a new one on me.

[suker]

It's useful ❕

Sent from my RM-939_apac_prc_200 using Tapatalk

[kstrauss]

Do you mean the Onsrud upcut or downcut bits? I don't see any newsletter info on their website. How do you get the Think n Tinker newsletter?

[GLCarlson]

Think n Tinker is at Precision solid carbide tools for woodworking and metal forming.. I'm sure there's a place to register for the newsletter.

Here's the link to what they say about O geometry cutters
micrO-flute 1-flute End-mills

As I said, new one to me, so I have no advice about what Onrud bit to use. TnT says theirs is "upcut". Since TnT only make small bits, I went looking for something bigger. Onrud seemed to be one supplier.

added: TnT is also a useful source of info about options for high speed auxillary spindles. I built a coaxial one for my 1100 using the DeWalt 611 and TnT's precision collets.