Cutting PVC Extrusion

Maybe if it is constrained from deformation it could be sheared?

E.g. If it is pushed through a hole the same shape as the section this will stop it deforming as a blade (or whirling knives) comes down whith imanse force and slices right through it with a satisfying noise. Ker chunk...ahhhh

Fortunately, cutting PVC stock materials is a rather common activity in the plastic business, and a good number of saw blade manufacturers have already solved this problem. Your results will improve if you have access to several pieces of information and or tools - how you approach may well be dictated by the arbor size and speed of the motor (and speed reduction?) available to you.

a) the saw blade design - several saw blade manufacturers produce a 'bi or triple tooth' style design - the saw blades have carbide inserted teeth that are welded on to the blade body - some are 'spade like - more pointed' and some are 'clean-out like' more blunted by slightly wider - in this way, the blade progressively nibbles into the material and then cleans out the sides of the cut. Blades having teeth slightly wider than the blade body are preferable.

b) the foot per minute (fpm) of the teeth moving through the material is important versus the size of your part, the wall thickness of any unsupported walls and the support given to the part while the cut is going on - saws with variable speed motors are best - often with multiple pulleys and belt reductions etc to be able to change the final arbor rotation speed - simple calculations in combination with different saw blade diameters should enable you to get into the right ranges -

c) just going from memory for rigid pvc, 4500-9000 fpm saw blade speed (sweet spot might be around 6000-7000 fpm if the product has about a .040-.050 wall typical) with a 80-100 tooth bi or triple tooth design blade with a slight NEGATIVE RAKE angle on the teeth in a 10-14" diameter blade will suffice - so depending on the arbor speed(s) available, the arbor size dictating the build of the blade, the diameter to put you into the right speed range, you should have good success. Additionally, these blades will cut many thousands of cuts before needing resharpening, and can be resharpened generally a couple times. I don't sell for any saw people, but an example catalog can be found at

http://www.generalsaw.com/resource/plastic.html

contains a general catalog – people "in the business" use blades similar to those described on pages 10 and 11 -

good luck

How about a hot wire cutter?

John.

I rather like the idea of the rotating knives, myself. Of course, a big threatening laser like any good arch-villain on James Bond uses would do, too.

Having 28 years in Extrusion profiles myself, I feel compelled to share some more information with the tribe if you do in fact feel compelled to move away from your currently inexpensive sawing methods -

a) the nichrome wire solution - unless you buy an off the shelf solution (source included), you are going to have to mess around a bit with the nichrome and a variable DC power source - amperage/heat/tensioning will be an issue - requires the wire or heated knife to be hot enough to part the part but cool enough not to get the sides gooey for the (guessing by sight) .040 wall - be prepared for some trial and error - and by all means provide some ventilation for the hcl gas that come from all PVC as it burns and degrades - there are heated knives that fabricators use for cutting sheet - not too wild about them myself - examples here:

http://www.ppe.com/ - look under "Heated Knives"

b) if you decide to go with a spinning knife style cold blade 'cutter' some tips -

c) you need some 'bushings' approximate the shape of the extrusion to keep it from deforming during the impact/torque of the cutting and shearing action that Del pointed out early on - (good work Del!). As the knife is rotated about an axis (like any single tooth on a saw blade or the shearing action not unlike a paper cutter) you are looking for either two support surfaces - one on either side of the rotating knife path, or one to shear against with the cutting action not unlike a desktop slicing paper cutter style movement. We always accomplished making cutter bushings with a wire EDM machine to burn a hole the shape of the extusion through the center axis of a 2 1/2" to 3" steel rod 6-8" in length, then part the rod in two making to pancake shaped disks and ground the faces that the knife would pass between perpendicular to the outside diameter (except for turning a slight chamfer on the circumferences for a 'entry' for the knife. An inexpensive way to do this is to take a couple of 2-3" long 'rings' of steel or other round metal material and convert it to bushings with a cental hole shaped like the extrusion in the following manner:

Turn the ring on it's side so that when you stand the profile up in the center of the ring, there is space between the part and the inside ring diameter - it is this air space that needs to be filled -

Do a little analysis to find one of the LARGEST parts in terms of overall size and thickness, and then add a layer of masking tape to all surfaces which approximates a part just a little bit bigger. You might want to then spray a little silicone spray on the outside of the tape to increase it's release characteristics. Suspend or stand the part (say 2 1/2 times the length of the ring) up in the center of the ring with a portion of the taped part held parallel in the inside central axis of the ring and fill the void with ordinary automotive body filler and hardener. Hold every thing square until the body filler sets and hardens. If this is a SET of bushings, align another ring on top of the first ring by aligning their outside diameters, and fill the second ring with body filler and hardener. Once all is set, pull out the taped profile and then use a grinder or sander etc to dress the 'face' perpendicular to the central axis and outside diameter (if you did one bushing) or the two opposing 'faces' of the bushing pair that a knife can now pass between. If you have done this, you will end up with a bushing pair that once held in alignment (line up as you set up with a part or two on the inside to align) will give you very nice support faces for a knife to pass between and good support on the part. You also will find that if you heat the part slightly (say to about 120-130 degrees F, the part will cut with much less torque requirements and still be under the approximately 160 degree heat deformation temperature of the material.

Now of course, all you need is a hot enough knife or a cold one moving moving with enough inertia or slicing torque to "cut" the part while it is at rest - and that's a whole different discussion.

Good Luck -

Jim Wilson

Nice post...

I like your way of making the bushings..that's sort of how I would have suggested doing it...but I didn't have the patience, experience or eloquence to put it into words!

Del

Carbide tipped (c4-c5) 60 tooth saw blade on 10" dia. using radial arm. I have found diamond to be very undesirable in the cutting of PVC - particularly viewing the image shown. A low mist spray cool or air cool may prolong tool life for repetitive cuts.

"I picked up my hammer and saw" said the blind man.

I'll vote for the hot wire. No fuss, no mess.

Use a portable band saw.

The band saw and a good vacuum attachment sounds like a excellent idea. On the other hand, Nichrome wire is made to get hot and retain its strength. You may want some sort of fume removal - not sure what hot PVC gives off. I do know, however, that many a model companies uses hot Nichrome wire for cutting balsa wood.

Hi geezer, the dust and extraction is the problem, ATEX approved is prohibitive for this application!

A high pressure water jet. No dust at all.

In the USA, there is a company that specialises in such equipment.....do a search with Google or similar!!

I think that it's crossed all our minds, but at only 500 cuts per day, the cost has got to kill them!!!

C'mon PlbMak... whadda ya think 'eh 'eh?

Is there a prize ?

Nice cup of tea or something... saucer of milk?

Yep, you win the Fruntkin Grabbler award for devious cunning!

Seriously, I think the link to General Saw from eagertask has been the most useful, So thanks to all for your efforts.

Cutting PVC with a hot wire will probably give off some nasty HCl fumes which you'll not want to breathe. Probably cutting at high speeds does the same but to a lower extent. In both cases you do need good ventilation.

You didn't say whether you want to cut during the extrusion process? or is the extruded profile at rest.

For in process, means the channel moves forward when you cut, we have mounted a circular saw on a table that moves at the same speed as the extrusion and cut manually. Overhead the saw we mounted a vacuum hood to take care of the dust and possible HCL gas. Works like charm, and cost less than a good dinner (with wine of course.)

Wangito.

Why not find someone who has a high-pressure water jet saw, or a laser saw. Those should make a very clean cut with a minimum of scrap and dust.

Any type of saw blade will cut vinyl. As a vinyl window manufacturer we use carbide tip blades because vinyl is abrasive. Use a blade to cut non ferris metals teeth have a negative rake angle of about 5 degrees. I recommend one with highest teeth count.

We cut a lot of our trim pieces on a 10 " miter saw. Most have a vacuum attachment shop vac will work well to eliminate the cuttings

You should try a blade similar to a meat slicer possibly with some water cooling depending on heat build up causing melting on the blade. It is a small cross section so should cut through fairly quickly.

You can find these blades used for cutting hydraulic hoses.

Garth, your sig is " Don't get on to the roundabout if you don't know how to get off".

Have you seen pictures of the UK's magic roundabouts?

You can actually go from one entry to ANY exit either going clockwise or counterclockwise, whatever the fancy takes you!!

This is only one of many around the UK, there is even one at Heathrow now I am told!

Ahhhhh the wonderful Hemel Hemstead 'magic' roundabout!!

It was built in the mid 70s and really cut down on accidents there, mainly because everybody was terrified of it!!

I love it as you can confuse the heck out of anyone by going the 'wrong' way round it....

John.

Andy, I transferred to Australia in 1971 so was not aware of the magic roundabout built in 1972. I thought you were pulling my leg and the Belgian bureaucrat's had finally forced the POMs to drive on the right hand side of the road at last, but apparently it works very well.

The Australians would have heart attacks faced with something like this they are still struggling with standard roundabouts unfortunately road building and planning in this country is about 15 years behind the so called 1st world country's

Please send engineers to Texas. That thing is way cool!

I am afraid that a lot of Foreigners get cold feet and turn around before the sign and try and find another way round them....but they are really good and really work.....

I have not a clue just how many there are in the UK now, but I know of about a dozen and I live in Germany since 1981!

Please remember that these are not small, they take up a large area, but do not add to any extra CO2 and require no electricity and could be left uncut by mowers if need be!!

Compare them to a traffic light and they win hands down....

There are a couple modest examples here and there. Massachusetts has a few I know of.

It's funny you bring up the other benefits. I was just mulling over the thought of how much good it would do if the city/municipals evaluated and corrected traffic signals that leave cars sitting waiting for nothing as they so often do.

Personally I run 'em when the coast is clear.

I hit the Swindon M.R. completely unaware of what was coming, following my mental freind, both of us on sports bikes. Aaaaaarg!

Since you work at a company that does extrusions I have a question. I have always wondered just how extrusions are made; tubing or whatever that has a hole, like your example. What supports the center part of the die to provide that exclusion? It must have something, but I can't get my mind around it. I'm not looking for an answer so I can build a product or work on my thesis, I'm just curious. It may be overly obvious to most, but it hurts my head to think about it. The product has to flow around it and then cool/solidify. Is that the answer; that that part of the die where the cooling/solidification takes place just hangs unsupported in the flow?

Kyoto, the centre hole, say in an extruded pipe is made by the die having a centre placed in the hole supported back where the material is fluid so that as the material is squished past the supports it flows around the central shape and out the hole to form a seamless pipe like extrusion.

John - correct me if I'm wrong someone!!!

You're right!

Oh thank you.... that makes a pleasant change then!!!

Sometimes I feel like Biggles, always being shot down in flames whenever I post!!

John.

Shall we inform others of your correctness? It always suit my missus well when it comes from elsewhere.

John...just though I'd let you know I've acknowledge your correctness and ticked it off on my huge wall chart with members names and their correctness scores !

(joking honest folks...it's a spread sheet really...no it isn't.. it's just a pigment of my imagination ...[deliberate malapropism folks.....funny I work with a lady who does loads of malapropisms..her name Spooner...no kidding...oooh my brain hurts now])

Wheres my valium?

Cat's most likely got his walls all marked up keeping score.

Right next to my dead mouse chart!

We don't make extrusion, I'm just trying to improve our cutting methods!

hey i saw a great documentary once where the guy had a cutting tool and it cut through loads of different stuff with no mess whatsoever..it was long and he had it in his hand and it cut arms off and there was no blood or anything...really cleanly cut...ah wait ..no that was STAR WARS...oh crap.

I saw one where a guy cut a shoe, then a metal pipe, then a BRICK, then thinly sliced perfect tomatoes. All that for $19.95 !! But wait, there was much much more!

Although water jet cutting is not cheap generally (and prices are hard to find with Google on a Sunday!), I still feel that the simplest possible water cutter has all the inherent qualities that they are looking for, except maybe price......

It is also possible that such a machine can also be used for other jobs that they do, so making the initial investment pay for itself sooner.

I would suggest that any processes that might be made or improved by water cutting, should all be intensively studied to see if the investment makes sense. ASAP.

Not to be argumentative but. Water jetting is way down the list, for this machinist.

Having assigned this task to numerous floor washing machinists to be in the past ,I gotta say again. Radial arm saw $200-$300USD (can be used on many other tasks) and a 60-80 tooth carbide tipped 10" saw blade ($100-150USD). It really doesn't get any simpler unless you push 'em through the band saw or use a porta-band.

Nuff said.

...in a sense I agree with you, but the dust of normal cutting processes was one of the original points that was considered obnoxious......which is why I continue to mention water cutting.

Please read the original post before replying.

I have read the original post. I have also spent a large amount of my professional life ensuring that tasks such as the one posted were accomplished. By the means I stated. Dust and all. A radial arm saw can be either purchased or rigged with a vacuum.

Have you ever used a water jet?

To be perfectly blunt, no vacuum system catches all particles. To use the cheap system that you suggest, would still require a mask. As with most of the suggestions up to now.

The water jet systems I have seen used are mostly overkill for this particular situation, there I fully agree with you, but if the system can also take over other jobs, as yet not detailed for us, then that still may be the way to go, in spite of price.

A water jet cutting system fits all the other prescribed requirements fully, no other system up till now mentioned, fits all these requirements.....the original posting person needs to come back and make a command decision.......also, price has not been mentioned up to now I believe, maybe it is "no object" on price?

If you really want no dust go back to my shearing suggestion (everyone else is repeating themselves so I thaught I may as well join in!)

Or you could always try shearing it! Quick, no noise, no dust, works on sheep too!

Actually Del, even your method produces a small amount of dust as well.....

The original person who posted this Blog needs to update from his point of view asap.

Picky picky picky....

yes, a dust mask should be used. appx .88 cents American for disposable.

OK. the dust is the issue here, as a diamond blade generates a fine powder; and little else; that turns out to be as potentially explosive as flour! This then requires a permanently fixed ATEX approved extraction system, which is serious overkill for this application. I'm tending towards the carbide tipped saw blade at the moment, as the swarf from this is a larger particle and thus won't come under the DSEAR assessment. Well, not as such a high risk, anyway, and should produce the quality of cut required. many thanks to all.

Ahh very good. So if these dust properties are an issue I offer the following. A very light, fine spray mist for cooling and dust control. A small cloth dust trap. One that will not be forgotten about, and is changed daily. I have had issues where when large amounts of plastic material accumulate the static charge crosses and shorts sensitive electronics, so don't allow to accumulate at base of unprotected machinery (as well as other hazards, such as fume and particle inhalation and potential for combustion). And then there is the issue of combustion. For the amount of material you are cutting you should be fine. the turbulence of the fine mist should keep gas from accumulating in shop and properly changed trap should resolve cuttings. If needed a telephone (free) consult with your local ESD expert could help.

My opinion. Opinion. For the amount of work being performed - use a saw.

I wish you well.

CR3

Yes Plbmak, all this talk of water cutting etc.... I'm surprised someone hasn't tried to sell you a laser cutting machine!!

If its only 500 cuts a day and its only a small extrusion, just employ a school leaver equip him with a hacksaw and a file then leave him to it...

John.

Hey that sounds like a nice stress free job...where do I apply? What's the pay?

Can you cut straight.

Can you cut straight?

When the Half-crown ceased to be currency in the UK... I took one and cut it in half

...(gave one half to my girl friend...ah..bless).

Oh...

by the way...

cut it the hard way

by hand with a hacksaw..

to end up with two discs, a heads and a tails......

So that's a yes then!

I certainly hope she appreciates the difficulty of that task! Was it a worthwhile endeavor?

Sadly not but we were young and she was a nice kid.

Oh the sweet innocence of youth!

So now we know who made all those double headed coins!

By the way, officer, cutting a coin of the realm in half is treason, you blackguard!

Mind you if a laser you want, it's a laser I can get. How does 40 Watts of IR sound? And also, have you ever considered the advantages of owning a really fine set of encyclopedia?

Im building my own set. They are also a vacuum cleaner.

Put your blade in backwards and use WD-40 for every cut. Buy a few "thin curf" blades and experiment. Use a sacraficial wooden spacer down the center of the piece to prevent vibration during the cuts. More WD-40 or silicone spray. Variable speed control with faster spinning motor or slower blade drop will also help. Simple and cheap.

I am gonna have to strongly disagree with the blade in backwards stuff. That is not a knee jerk response rather a point of tool life and my inability to be comfortable throwing money in the river unless I am at the casino.

PVC is is a thermoplast. It is also surprisingly abrasive. The method described is going to generate a lot of heat. Not good for a thermoplast. It is also going to generate a lot of mess. It is also going to generate a lot of resistance from anyone who ask the inevitable, " What the heck are you doing?"

There are many people who confuse carpentry with other manufacturing principles. At times I say things that allow everyone around me to question whether or not I have any idea what I am talking about. It is nice to see that I am not the only one.

Hi gang - sort of lurking on this thread and like the mix of sound engineering and creative 'nutsing'; would like to offer a few more opinions - always free and worth exactly twice the price . . .

a) the concept of 'blade in backwards' is the confirmation that a negative rake or tilt to the blade teeth imparts slicing versus gouging action - agreeing with negative rake, disagree with use wrong blade creatively - just buy the right kind of blade to start aka carbide bi- or triple tooth design, with 5 degrees negative rake - blade won't have to be sharpened for many cuts, and then can be relatively cheaply. Yes, PVC is slightly abrasive, generally due to the loading of talc or calcium carbonate used as fillers - sometimes in color packages, and UV stabilization packages. By the way, do your production folks a favor - remind them to remove jewelry - particularly gold and silver rings while handling the slightly abrasive PVC - you know those grey marks they leave on the PVC? (come'on you want to test it right? Just rub a ring on the surface . . .) - yup, thats GOLD and SILVER being worn away - adds to the phrase 'value added' - eh?

The sawn material removed will be much larger than dust. Inexpensive paper dust masks for the chips (which won't be much given the small size of the part and an inexpensive 'catch box' behind the chip path to catch 80% of the chips) and more importantly in this case, eye protection are always a good idea in a shop environment as well as a "Lock-Out, Tag-Out" procedure to disconnect all sources of danger when installing blades, doing set-up, and servicing the equipment.

b) Recommendation - do not put petroleum products on PVC in general - depending on the application, the by-products in the can (aerosol propellants etc) can create a variety of problems including UV and color fastness failures, and negative interaction with mating parts (not previously mentioned). If your final installation (what ever this does) needs to be warranted by you, not a good idea to create a future problem.

c) - good old "silly-cone" spray; next to WD-40 and duct tape, another of the great 'cure alls" - falls in line with 'Bash to fit, Crush to assemble, Paint to hide' axiom <snort> - this is generally not a good material to be used in a shop environment as it will get into (and onto) everything eventually (worst is the floors and assembly counter surfaces) - again, if used on and impregnated into PVC can cause other problems - especially if you later want to use any adhesives with gaskets, tapes, labels etc. As someone who warranted PVC products 'in the field' for 25+ years, it is not a good idea to spray, coat etc other stuff into your base compound; bare minimum it will VOID the warranty from your PVC profile supplier and their raw material manufacturer.

Hopefully you have already used the information to acquire the correct blade and are producing satisfactory results.

good luck

Jim Wilson

oops - wasn't logged in - sorry.

Jim Wilson

Konichiwa, try Samurai Sword PlbMak san.

I have heard that rodents will chew right through PVC. That's what I've heard.

We ave several moduls, an zay all work a very fine!!!

I'd heard that Alice Cooper had lost some stage gear....

The only Katana I've experienced had 2 wheels and an engine...

I was going to suggest a shear, then I saw the guillotine. Just how much does a shear cost anyway?

If you go the reversed circular saw blade do NOT use a carbide tipped one. The teeth will come off at the most inopportune time. I was cutting polycarbonite panels with mine and it was working fine until too late I realized what it was that was that was flying around. One flew off and impacted against my double insulated glass sliding door. As I walked away I was confused by the the sound of ice crunching. Went back and saw that the entire outside glass was crazed. As I stood there looking at it, I marveled that one of those things didn't go in my eye. Yeah, I know, beat me up on not wearing my safety glasses.

There is no need to beat up on you for that, as anyone over the age of 12 must usually learn the hard way......humans.....!

But you would have beaten up on yourself if it had happened, or as close as the bandages would allow!!

I also feel that the saw blade you were using was of awful quality.......I have never heard of that happening under normal usage before......was it Far East quality?

No it was a quality blade; a Freud. They just aren't meant to cut backwards. Guess I wasn't thinking and since then have always used a regular plywood blade turned in reverse. Makes a smooth cut. Works great cutting plastics; doesn't rip the material and cause it to crack, kind of grinds through it nicely.

As to the lack of glasses, I was wearing my regular glasses, just not safety ones. Wasn't totally stupid, just partially.

Thanks for the explanation...

I have heard more of this nonsense of backwards blades than I can stomach.

Having spent years in a plastics shop I just don't understand why people would do such.

This would explain much. Like that little loss of consciousness at the end of your sentence.

The difference is in breaking the product or cutting it. When making indicator light covers for spreader bar light boxes for our container cranes, we used different colors of Lexan plexiglas. When using a circular saw, the Lexan would always, ALWAYS crack/break no matter what we did. Finally one of my coworkers who was a pretty good woodworker, suggested reversing the blade, it worked perfectly and we never broke another piece. So, sorry about your stomach but this worked for us and worked flawlessly for me on the polycarbonate.

Yeah I'm just spoiled. I do stuff right. I use a sharp blade. Cut slow and cool. Oh, yeah , I router finish and flame polish critical edges.

Yeah my stomach, hmmmm, that could be from years of cheap whiskey.

At those velocities, I doubt your safety glasses would have been of much help. Nor would the front or back of your skull as the tooth passed through your head.

Your a lucky man! So, what are the six numbers for this week's lottery?

OK. Hear me out on this one...

I'm thinking about after extrusion, you spray the molding with a mix of silicon and chicken broth. As the part moves down the line, it come to a strapped down crocodile, which is constantly being agitated by your apprentice. As the plastic (coated with silicon and chicken flavoring) passes through the crocodile's open mouth and across his tongue, he will instinctively bite down, cutting off the appropriate length.

Let me know if you need diagrams for this.

Idont know about need, but post those diagrams!

would that be like an a.m.e drilling a hole in a cockpit window,or polyfusion welding

where the pipe is cut with a chainsaw that has its' teeth ground to a different Angle of attack.