View Full Version : ideas about CNC for making Vacuum forming molds

Mike S-H
12-14-2006, 05:27 PM
Can anyone suggest what kind of CNC device is the best to make molds for vacuum forming. Forms max size is 600 mm х 600mm х 100mm. We do really dislike to waste shop space/ money for large size machines. Is it possible to treat wood on steel CNC vertical machining centers and vice versa.

12-15-2006, 09:54 PM
The biggest challenge to mixing wood & metal machining is the metal requires coolant, and wood is cut dry. The wood sawdust hits the oil, and won't go away. You can do it, but you should put a vacuum cleaner at the cutter to pull all of the sawdust out so it won't gum up the slides and bearing surfaces.

08-20-2007, 10:51 PM
We cut all our own patterns with cnc bed mils(milltronics) Just have to clean machine off after milling is done.

08-21-2007, 09:48 AM
I know of some high speed graphite machines that are for sale and run 25,000 to 30,000 rpm spindles, and 1600, to 2000 ipm. This would be perfect to cut wood patterns. I have made several blister tools in the past. These machines will even cut hard steel easily up to 60 rock well C scale. They are extreamly accurate when new .002 um. tir. used you could buy them for pennys on the dollar and they would be way more accurate then your blister tool would ever have to be. They do not use coolant and come standard with 2 large 6" dia. vacume hook ups. This was to pull off the graphite dust. They also have constant air blow hooked up to the M control on the machine. They run 160i, 160mc, or 150i Fanuc controls on them. Let me know if you are interested in them and I will hook you up. gsilberberg@progressive-plastics.net

08-21-2007, 10:00 AM
Most CNC Milling machines cannot machine wood because wood requires high RPM (18,000 to 24,000) and very high feed rates from (200 ipm to 800 ipm). Most metal cutting machines are not equipped to do this. Plus wood requires different Tooling altogether. Like down cutting bits so your wood will not chip out. Most Up cutting bits do not work well with wood. They do, but not well. Plus like the others stated, you will have a big ole mess to clean up what with the wood chips and dust every where.

08-21-2007, 10:09 AM
I agree with Boots on the rpm issue, but wood doesn't make the highest quality vacuum forming molds anyway. You will get grain telegraphing on some of the work. Renshape is the material to use and it will cut very nicely with lower tool speeds.

08-21-2007, 11:16 AM
We rough out our pattern using 1 inch carbides,4 flute,.600 deep@600 ipm,6000 rpms.The finish cuts use solid carbides,4 flute anywhere between 350 to 800 ipm 2500 to6000 rpm's.When we take our pine patterns off the mill the're as smooth as glass, but when sampling they will leave grain bleed thru. mdf,renboard also do well without the grain bleed thru. We run anywhere between 20 to 50 sample parts off these before sending them out to be cast. If you're not sending pattern out to be cast and your going to run a big order use renboard.

08-22-2007, 07:54 AM
You can get a better and cheaper material than ren wood. It is the same formula as renwood (ceba), but much better quality, with out voids (air pockets). It is a place call BCC products in Franklin Indiana. Ask for Roger Jr. We have used this material several times and the cost is lower than Ciba the last time I bought it.
Boots many of the new high speed graphite and steel cutting machines run past the rpms and feed rates you were talking about earlier. for example Roku Roku, Okada, Makino, Roters, even Hurco has a 20,000 rpm machine. I am sure Haas has one alson.

08-22-2007, 06:11 PM
yes yer right there jetski the last Mori CNC vertical mill we purchased had the option to purchase the High Speed Spindle. But we didn't see the need for the extra cost. But the way they are designing Tooling for these machines these days is radical. The speeds and feeds are going up.

08-22-2007, 10:22 PM
How does this other material you mention hold up to heat? We form a lot of .350 and .4oo gauge material so you're looking at 6 to 8 minute cycles.
I know the ren 550 gets a little soft after a few parts and we have to let mold cool off.
There is one thing I don't like about the ren is vacuum drilling, you pull out the drill and it seems to fill back in, you have to run drill in and out a few times to make sure you got a clean hole.
What is the max.size pattern that can be milled on a Hurco?

09-09-2007, 01:06 PM
Does anybody out there use small cheap CNC machines to make large vacuum forming tools in pieces, maybe from MDF, and then fit the pieces together to make the tools?

This seems to be a good way to leverage some of the relatively small CNC routers out there, letting you vacuum form bigger stuff than you can cut directly. (You could even make pieces deeper than the CNC machine can cut, by stacking.)

Any problems with this approach? (It's something I'm tentatively planning to do, but not soon---I don't have the CNC machine yet.)

I can imagine that you'd wear a little machine out if you did much of this, and it wouldn't be cost-effective in the long run, but for just a few big items, it seems like a good way to go.

09-09-2007, 02:12 PM
..... letting you vacuum form bigger stuff than you can cut directly. (You could even make pieces deeper than the CNC machine can cut, by stacking.)....

And if you were really creative you could make collapsible moulds; separate components around the periphery with a tapered plug inside. Then you could vacuum form shapes with deep undercuts and remove the mould from the part in separate pieces.

09-18-2007, 09:34 PM
Hi all!
We recently converted a Atlas Knee mill to CNC. We also ran into the problem of needing higher RPM's for our wood work. We simply mounted a Router motor on the Z spindle. It takes less than one minute to change from steel to wood. It really makes the machine very versatile.
It takes longer to clean up than to change it over.

One of Many
09-19-2007, 12:44 AM
I have designed many of this style die. I called these "pull off's". Sections of the die could set on tooling points, taper pins or nest cradles within the larger form. As the part comes off the die the operator pulled all the add on blocks out of the molded part placing them back on the die ready for the next cycle. I thought it was pretty common practice in the industry. 2-4 pull offs wasn't too bad, but a few I made were in the 10-12 range and dang it if the forming department didn't complain after a run of several hundred of those cycles hit the shop floor! LOL!.

There were also parts I designed that we formed directly over structural plastic extrusion and other objects with the intention of trapping the skeletal part inside the formed part. It's coming off anyways, so big benefits if you sacrifice part of the die that contributes to its form and function impossible to produce otherwise.

There is realistic and then absurd, but if the customer is willing to foot the bill for the additional cycle time, eh.....you may not be able to afford to turn them away.


09-19-2007, 11:03 AM
DC, I'd be interested in hearing more about the multi-piece molds and stuff you made with them.

Also more about forming around structural members, and leaving them in.

That's the kind of thing I eventually want to do when I actually get a CNC machine to make relatively fancy molds with.

Do you have any pictures of your molds, or parts made with them?

Any rules of thumb about partitioning shapes to make the multi-piece molds work, and how to take them apart to get the part off?

I've been toying with several ideas, but they're all pretty cumbersome.

One of Many
09-19-2007, 03:56 PM

This was 15 years ago, so I don't have pictures, but I do know parts are still being formed on many of my dies at the same facility.

These were aluminum dies for anything from dental chairs to radar equipment covers. They could be hand pulls, logo's, cosmetics or strengthening ribs. The pull off's were still a basic forming die with side draft to help release the die easier. It just seated or located on the side of the main die in any convenient fashion but still allow vacuum to pull in behind and through it. The back side of the die and seat it rests in must include draft so as to keep the dies from sliding against each other as the part is separated from the die. I placed holes or hook pulls in the back side of the dies. After forming the operator could use some crude tools to pull the dies out of the part and set them back in their respective seat. On some cast dies, the walls were rather thin so the draft was minimal on the pull off's seat. I would bond acid etched teflon sheet to the main dies seat so the pull off wouldn't score on its way out.

There were so many parts that I had made with structural inclusions. Hmmmmm(think, think)

One I recall was a snap over magazine holder for gym equipment consoles. Maybe 10"x20" parts? A full radius the length of 2 long sides were pull off dies. A piece of 1/8" aluminum plate stuck straight up out of the die about 2" tall which we placed ABS extrusion onto that left with the part. See my cheesy detail included looking into the back of the part. Of course my quick little sketch there is of the part after trimming so you will need to use some imagination what the formed part looked like prior to trimming. We made 10's of thousands of these things in several sizes and configurations. The customers part volume grew enough to warrant injection molding.

Plenty of others, but I'd rather not highjack this thread to far off topic.


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07-22-2009, 08:37 AM
How does this other material you mention hold up to heat? We form a lot of .350 and .4oo gauge material so you're looking at 6 to 8 minute cycles.
I know the ren 550 gets a little soft after a few parts and we have to let mold cool off.
There is one thing I don't like about the ren is vacuum drilling, you pull out the drill and it seems to fill back in, you have to run drill in and out a few times to make sure you got a clean hole.
What is the max.size pattern that can be milled on a Hurco?

Coonhunter Bcc in Franklin Indiana would have the specks on the material. We never put heat to it. Always used as a pattern or a model and then trace milled. Ask for Roger Jr. @ BCC many materials and great information (owner and son). Max size on a Hurco is on their web site. If it was me I would get one of the large enclosed machines to cut wood. Keep the saw dust in a confined area. Thermwood in southern Indiana makes huge cnc routers kinda expensive. CNC mills are not free either though. Torit make a great dust collector, I have used a 1700 cfm unit in several shops for years with graphite cutters and it keep the machine ball screws and ways cleaner. 1700 cfm will pull you through a key hole with the doors closed on the machine, (dislocated both shoulders one time this way, good thing I had my cresent wrench in my pocket or I would have went all the way through the key hole) LOL. If you can keep yourself 4-6 feet back from the key hole you can work naked and not need a date later that night. By the way I was fired from that job too. So not that I am 50, beer gut, balding, and by the way "Drop Dead Sexy", and on blood pressure meds I keep back from the machine when it is running so I don't have a blood shift and black out. Have fun out there guys. I am just a fun loving tool maker. If you are wondering about the jetski name I rebuild trashed ones for fun, and there is a lot to be said for the thrill of going 70 in something the size of a bathtub. I think if I could put a Harley motors on it my wife would enjoy it too. Well back to tool makin