View Full Version : Having terrible results cutting pvc pipe....

12-01-2008, 11:54 AM
Hey guys, I'm trying to cut pvc pipe and I'm having alot of chipping out. The hold down is tight...Here is the Jig


And here is a pic of a piece that is chipped out.


I've used 1/4" upspirals and down spirals at all diferent router and move speeds, and I've used a half inch straight cutter....Any suggestions?

12-01-2008, 12:17 PM
Try an o-flute bit. They are made for plastic.

12-01-2008, 01:08 PM
Are your parts tearing out only on the "exit side" of your passes? If so you could do what some 'Botters do for dovetails and set your first cut up so that you enter the part from the outside and cut toward the middle, and then move the bit to the other side and do the same. That should give you a little more "meat" to work with...
It would also place any tear out in the waste area of the parts...

12-01-2008, 01:46 PM
Hey Guys, I would like to use an o-flute, they always seem to work well. The problem is I need a Inch and a half of cut length, and 1/4 inch Oflutes arent that long. I do see that 1/2 inch diameter Oflutes are longer but there pricey and I'm still not sure if they would work.

Bill, the bit seems to enter and exit just fine. The chipping occurs as its already cutting down the edge.

12-01-2008, 02:01 PM
Can you post a screen shot of your toolpath?

12-01-2008, 03:02 PM
Try an onsrude 52-622 I just used it to cut some acrylics and it cuts realy nice .

12-01-2008, 03:46 PM
My tool path is a inside profile using part wizard. I've used both conventional and climb milling options. Its done in a single pass. These sewer pipes are thin walled material, so that makes them some what brittle. Does anyone have another Idea on how to cut the square out? I imagine most botters would try and use their machine as I have....Its the only way I can think of.

12-01-2008, 04:04 PM
looks to me like your problem is the material bouncing at the cut.
maybe slow down your feedrate,
or find a way to support behind the cut?
can you use a thicker wall?

good luck

12-01-2008, 04:54 PM
It might take a tiny bit longer but if you plunge down the center and remove the inner material working your way outward the material would remain solid. Final outline could be done at a different speed (or direction even).

Good Luck.

Brady Watson
12-01-2008, 05:24 PM
Those hose clamps may be distorting the upper portion of the pipe, even though you went thru the trouble to make a nice cradle for each one.

One thing that I know will work, although they will be sacrificial, is if you make several circles out of MDF etc, the same size as the inner diameter of the pipe. Give yourself a little bit of allowance (say .004" smaller than inside dia) and slide these in where the cutting will be on top. Even though you may have to replentish them after each cut or so, I can pretty much gaurantee that you will get clean cuts. The issue is not the cutter or the speeds, it's the material deflection. Use the inner 'pucks' along with your clamps to keep everything true while cutting. A wooden dowel (if you can find one the right size) would be ideal.

I would try ramping into each cut, using a downcut tool if posible, and set MS @ 1 IPS to start, and RPM @ 13000. If you get excessive melting, then try increasing MS to 1.5 IPS. Play around with Climb vs Conventional until you get the best cut. If the material is still shattering, try jacking the RPM on the spindle/router all the way up. You might get some melting, but see if you can cut without shattering. If it works, back the RPM down until it starts shattering again, then go up a little (changing nothing else).

You may want to try a regular old 2-flute straight bit instead of the spirals. This will neither push nor pull the material up or down while cutting.


12-01-2008, 05:33 PM
I'd try cutting the sides (parallel to the pipe length) first, full depth but approaching from the outside, starting with a light cut with the corner of the bit just scoring the pipe first, then a little more, then just barely all the way through, then go on to the cross cuts.

Another approach would be to start as I just said, full depth, parallel to the pipe length, back and forth removing the entire area as you work across the width of the pipe instead of just an inside profile. Then do a final clean up pass on the ends of the opening. Trial and error will tell you how much you can take off at once.

12-01-2008, 06:38 PM
You could have big wood dowels turned to fit inside, then screw the cut away to the dowel. This or dowels plus tabs should help a lot.


12-01-2008, 08:34 PM
This is similar to the problem i had trying to cut hollow spirals. And as others have stated here, how i solved the problem of not cracking the thin wall is to turn a sacrificial inside dowel that fits snugly on the inside diameter to keep the thin wall from vibrating. Cut thru the pipe and wood and use a straight flute cutter. I got a nice straight flute cutter from Centurion and i thought Fred told me he had them in 3" lengths (I could be wrong but check the website).
It is important to use a straight flute because the spirals (up or down) seemed to want to catch the spirals and I got vibration and broken spirals with them but not with the straight bits.

12-02-2008, 12:13 AM
Cool, Thanks alot guys. The only think I'm worried about is how long the dowels will last. I'll definitly get a straight cutter. I have to mass produce these pipes by the thousands hopefully. Here is my product....


12-02-2008, 02:38 AM
The front wheel of a marine bicycle???
A ferris wheel for gerbils???
A mid stream electrical generator???
(Yeah it IS early.....).

12-02-2008, 03:15 AM
Just rotate the dowel a quarter turn till you use it 4 times then get another.

Gary Campbell
12-02-2008, 04:41 PM
You should be able to reuse the "dowel" as many times as needed. It is there to stop deflection, doesnt matter if it has a few cuts in it, or you could put it in the exact same spot every time.


12-02-2008, 06:08 PM
Thanks for the help guys. I got a double flute straight 1/4" bit and it seemed to do the job without the dowel inside. It wasn't perfect but it was good enough for my prototypes.

I'm thinking that the way to do this at a production level would be to use dowels inside and some kind of blade/punch type system...

Any thoughts?

12-02-2008, 06:16 PM
Another thought might be to screw the cut-out/scrap piece to the support dowel, then remove it after the cut. That would rigidize everything to eliminate chatter etc during the cut.

12-02-2008, 09:43 PM
Daniel I deal with pvc every day and some can be quite brittle.If you've bought it from a place that stores it outside the sun can deteriorate it And make it easy to break.


12-02-2008, 10:18 PM
What is it?

12-03-2008, 10:01 AM
Hey Guys, The screwing the scrap to the dowel is not really an option. If I am making thousands of these pipes you can imagine how much time and labor that would create, I'm thinking that this is one job not suited well for the bot. I get the pipe from lowes where its stored inside, but who knows where they got it and how it was stored before they got it. The whole assembly put together is a hydroponics system. The plants revolve around a light that goes down the center.

12-03-2008, 11:46 AM
Uh-oh, plants and lights for indoor growing

For the production parts, I would look for a shop that has a laser tube miter machine. The local rep from Tube Service Co. came in the other day and showed us a video, amazing machines. They could probably pop out 1000/day.


Brady Watson
12-03-2008, 03:24 PM
You are not supposed to use a laser with PVC...the fumes are quite nasty & I believe that it will plasticize the laser optics with the smoke that comes off...

The worst thing that you can do is give up. I've cut PVC pipe a number of times on my Bot, so I know it can be done. It is only a matter of doing some R&D on your end & carefully observing what is going on while the machine is cutting. It will tell you what it needs if you listen in the right way (not trying to be smart...observation pays off).

Part of your issue is not having control over the toolpath. Just running, let's say, a 2" end mill thru the side of the pipe is not the most elegant or efficient way of cutting this part out. If you are able to hold the part down well - you *could* have someone generate a toolpath for you that follows the contour of the part, stepping down in let's say 2 passes, with the bit only going into the pipe 1/2 the wall thickness per pass as it follows the contour. This is something that can be done easily in ArtCAM. If you are cutting out thousands of them, then it would be worth your while to invest in whatever it is you need to get the job done.


12-03-2008, 04:32 PM
Cool, Thanks for the tip Brady, I agree that the tool path could be optimized to do a cut in an arch type pattern in the xz plane. I'm not exactly sure how to do this. Also the jig I created was originally intended to be used for vaccum, however the FeinIII was still not enough to hold it. Maybe if the toolpath was optimized as stated above it would be fine, if not, then its possible that if I get two of the vac motors from your open source vac system, it might hold well enough to do away with the hose clamps. I will post my part wizard file soon, and possibly someone could qoute me a cost on optimizing my toolpath.

Thanks again guys!

12-03-2008, 04:50 PM
I'm thinking that vibration of the material around the cutting tool is the problem. You have a nice saddle on the bottom side of the material but that is not where you are cutting. How about a saddle for the top? The first time you use it cut through the saddle and the material, then reuse to hold the material down. Actually - how about you cut a heavier gauge PVC pipe of the same diameter down the center lengthwise and install it as a top "saddle"? The pipe clamps would hold it in place - again, cut through the whole mess the first time and reuse.

12-03-2008, 08:08 PM
Maybe you could see if you have someone local who could waterjet cut it? If it was cut from the side as opposed to the top it could be cut that way on a waterjet.

For that matter if you get a long enogh bit you could cut it from the side on the bot similar to the toolpath illustration here. I know its a crude drawing but...oh well..


12-03-2008, 08:46 PM
I cut slots, round holes, sq holes in PVC pipe all the time with no problems. For the sq holes I use a 1/4" Belin bit. The difference is, I mount the pipe in my indexer with a tail stock to support it. I rotate the pipe so the longitudinal cut is on top, cut that, rotate to cut circumferentially, cut longitudinally and rotate to finish the cutout. this way the cutter is always perpendicular to the surface being cut. The cut is excellent.

12-03-2008, 09:37 PM

I guess I assumed that a production run of thousands of parts might use something other than Lowes PVC
Sorry, didn't have enough coffee...

ABS can be cut with a laser, is the ABS sewer pipe the same as ABS sheet??

For prototyping and proof of concept, you can't beat the bot and trial and error.


Brady Watson
12-03-2008, 10:51 PM
I forgot where the stuff came from
There's no reason the stuff can't be cut on the Bot. I visited a boat manufacturer one time & they were cutting 4" PVC pipe into fishing rod holders for a 46' dive boat. The guy was using a template and a hand router...

The only advice I could give at this point is...Don't give up. You'll figure it out if you are persistent enough.


12-04-2008, 03:39 AM
I've done some similar work and my experience concurs with Terry Kovacs post above.

I would make a "top" version of the jig you already have. The top would have holes cut through it to match the cuts you want to make in your pipe. Machine the pipes within the holes, pop the top off, reload, and your all set.

Clamping the pipes between the two halves will hold the pipe from moving, give you support against stress/cracking, and keep the pipe from deforming from round while you make your cuts.

The added mass of the jig top will also cut out vibrations in the thin-wall tubing - eliminating this chatter will improve the finished cut quality.

12-04-2008, 09:36 AM
Hey, thanks alot guys. These are all great suggestions and are going to help considerably. Using the 1/4" straight bit has already helped. I believe my next step will be to create a top to the jig as Terry and Russ have suggested and then use a toolpath that follows the contors of the pipe as brady has suggested...I will defintly upload pics of the results....

12-04-2008, 10:47 PM
instead of wood dowel how about that pink styrofoam or the white. just push the pvc into it. that may help and would be a lot quicker them cutting dowel to fit and maybe cheaper. I'm new at this but also is it possible to run the bot in reverse like when cutting siding butting the blade in the saw backward.

12-05-2008, 11:22 AM
Why not try something like this:


This is basically a dowel with sized inserts along the center to support the area where you're cutting. Might be too big for your purposes though...


12-05-2008, 04:21 PM
Hi Daniel, interesting design. Brady is right, don't give up on conquering this. How about altering your jig to hold the pipe better closer to the cutout. The clamps you are using are still letting the pvc vibrate and chip out and giving a bad cut. If you made a top (lid) to your to your jig it would hold the pipe down snug and also support it around the area to be cut out. The lid must support the whole piece of pipe and not just the areas on the ends as your clamps are. You have a nice base made for the bottom, just make a nice one for the top, hinge it to open up and put some clasps on it to lock it closed during cutting. It will end up having your cutout in it as well but will support the outside of the pipe from chipping. If your pipes are precut lengths also put in some endstops to lock it in and reduce chance of end movement. Try making one to troubleshoot and perfect the design. Abit of time perfecting your jig will be worth it in the end. Keep us posted

12-08-2008, 02:47 PM
Thanks guys! All great suggestions! Here is the layout of the pipes in the jig...


You'll notice the square cut out with the two rectangles inside it. These are cut on oppisite sides of the pipe a shown in the pic below...


So basically, I need a toolpath that that utilizes the z axis in order to does this in two nice pasess...So who should I email for a qoute to Generate a toolpath? Brady?

12-08-2008, 03:02 PM
I have a few more questions about manufacturing my product, if anyone cares to comment. I'm trying to figure out how I would go about manufacturing a thousand of these if I had the demand. The Black tubs where vacuum formed on a very crude machine my partner built just for our R&D. We now have quotes from a local company about doing it for us. They will deliver a finished tub for less then we pay for material right now, the draw back is would have to invest a total of $7000 to get to aluminum molds cast.
So we have that part figured out...

The part still up in the air is how to manufacture the parts for the wheel. My major concern is that the acrylic and the pvc are very sharp when the machining is over. Knocking the edges off all the parts would be very time consuming. Is this where a Laser would be useful? I've heard parts cut with a Laser are not sharp. We could possible swap the pvc pipes for some kind of abs pipes that can be cut with a Laser...Any thoughts?


Brady Watson
12-08-2008, 03:35 PM
Send me an email with a CAD drawing of your part & the outside diameter & wall thickness. I'll be in & out this week, but will try to get back to you ASAP.


12-08-2008, 04:15 PM
I don't know what you've already tried for treating sharp edges on parts, but you could flame polish the edges of acrylic parts - not sure if you could do the same for PVC.

You can also use a buffer - there are many different types of wheels/heads and many different grits of polishing compounds. The right combination makes a lot of jobs easy.

12-09-2008, 07:14 PM
Daniel, interesting product and fabrication challenge.
Your most interesting point/challenge so far to me is...
"I'm trying to figure out how I would go about manufacturing a thousand of these if I had the demand."

As far as I know, there are many qualified botters out there all looking for business and have capacity. Stir any ideas?

Develop your material and process lists, reach out to folks who you can qualify, certify, and verify their set up and results.
Determine a fair cost to be competitive and successful, and give folks some orders to make it happen.

I call this "distributed manufacturing"
Spread the risk and reward and seek higher volumes, lower material and process costs, and focus on building the market demand/volume.

Diligence + an intelligent business model should propel you toward success but you don't have to do it all yourself. That model has it's limits and they are generally like the "starving artist" model. Great fun and self satisfaction but poor diet and cold living conditions.

Best of luck and don't eliminate the distributed manufacturing model.

Just a thought.

12-14-2008, 02:10 PM
Ok Guys, here is an update on my pipe situation.
First of all I am using a straight cutter, and a toolpath that follows the contours of the pipe. I have also installed wooden disk in the end of each pipe under the hose clamps. This keeps the pipes from distorting when clamped.

My results are much better, but the pipe still doesn't like to be cut. Here is a pic of my results..


Still Jagged, but not chipped or split. Here is after I cleaned it up with a file...


So, I'm going in the right direction.

Does anyone think that abs plastic would cut better? If these were made of abs, could they be cut with a laser?

12-14-2008, 02:27 PM
Good to hear that you haven't given up and that you're making progress...

I'm still standing by my earlier recommendation for adding a "top" to you jig. I've cut thin wall pipe with jigs like this before, so I can tell you that they work and that you don't need a laser or different material.

If this were a flat sheet of thin plastic being cut in mid air, you'd run into the same vibration issues and you'd have the same cracking/poor cut quality. The type of bit you cut with/cut path wouldn't change the results all that much. 90% of the solution is in the hold down fixture.

Best of luck!

12-14-2008, 03:15 PM
I still stand by my suggestion earlier that you need to have a snug wooden dowel under the cutting surface to eliminate the still evident vibration which is what is causing your jagged edges. When i was doing my hollow spirals, i broke more of them till i figured out to put a reinforcing dowel inside and haven't broken one since....

12-14-2008, 04:24 PM
Have you tried schedule 40 pipe. It is thicker and should not vibrate as much.

12-14-2008, 04:47 PM

Brady Watson
12-14-2008, 05:48 PM
I bet if you did the previous operation with some allowance & then come back and do a final pass at high RPM, you would get a clean cut. You can cheat a bit with high RPM on thin-walled materials by reducing chipload, and in turn, vibration from the tool grabbing/yanking the material as it cuts.


12-14-2008, 06:43 PM
I'm with Neville on the indexer. I have an Epilog laser and even with the attachment for working on round surfaces (like wine glasses and bottles) the laser is incredibly slow. Plus the laser beam, if the power is set high enough to cut through thick plastic, may continue on and ruin the back side of the pipe.
I cut lots of plastics with my laser but PVC is a definite no-no for a number of reasons. I have a purger installed to keep my neighbors happy but even that is no match for the smells plastic makes when laser cut.
With the number of pieces you are looking to make, I should think you could easily justify the cost...


Brady Watson
12-14-2008, 06:56 PM
I agree - an indexer would be ideal for this part, but the toolpaths would still need to be tweaked to get the right cut quality.


12-15-2008, 12:53 AM
Hey guys, The indexer had crossed my mind as well. I will need to become educated on the indexer hardware. I have a very limited budget, so I probably can't buy one. What I do have is lots of time, an old wood lathe and a partner who can weld and fabricate like no one I've ever meet. So maybe we could build one and only have to throw down $400 for the stepper motor. Does the motor hook directly to the chuck or is it geared?

12-15-2008, 06:57 AM
Does anyone have any good pictures of an indexer installed? I would like to see how it actually works on a Buddy and what space limitations we would have. We drive the PowerStick with the center motor. Why couldn't we harness that to drive the indexer? The size of Daniel's part makes it a good one to experiment with...


12-15-2008, 04:14 PM
Have you considered a vacuum pump-style vacuum jig that holds from the top?

If you don't want to invest in a vacuum pump, what about multiple passes with a 1/8" bit.

12-15-2008, 10:46 PM
Here is my indexer installed however it is not on a buddy, if that helps any...


Gary Campbell
12-15-2008, 11:21 PM
As JAck says, these are not on a Buddy, but a lot of info here... and in the rest of the Indexer Section of the Forum. http://www.talkshopbot.com/forum/messages/33571/34430.html?1223404686