# Selecting a CNC router for 3D mold making



## DsKnees (Mar 4, 2021)

Hello all,

Today I got a quote for having some molds professionally machined. Turns out it would be nearly $1,400 for a 23"x30"x4" mold, machined polyurethane tooling board. When I opened the quote, I realized that buying a quality CNC router and doing the work myself would save me an awful lot of money! (Plus, once I figure it out, I can get it done on my schedule, rather than waiting for other people.)

The molds I am making are for carbon fiber parts, and the material I plan to be working with is likely to be polyurethane foam tooling board, or HDF. (I hear MDF isn't much fun to work with.) 

For specs, I'm looking for something in the 2'x3' to 2'x4' range. I am trying to start a company making carbon fiber knee pads, which are fairly small, so accomodating larger work isn't an important consideration.

Budget is kind of whatever it takes, but realistically less than $10k. It hurts a little already to think about, but I think that's about where I need to be to accomplish the work I am trying to do.

And lastly, getting the most z-axis travel is one of the most important considerations.


The most promising machine at the moment seems to be the Industrial CNC Short Cut 203. It has the most gantry clearance by a significant margin.

Shop Sabre 23 looks like a solid machien, but gantry clearance is listed at 5". It says "5" (standard)", so maybe there is a taller option?

CaMaster Stinger I looks solid, but also 5" gantry clearance.

Grizzly has one, but is only 5" from spindle to table

Well, I guess that's my short list right now. I'd love to find out if there is a better option that I haven't come across yet? 

Any experience with these machines? What would you choose? How would you prioritize the array of options available?


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## old55 (Aug 11, 2013)

Welcome to the forum.


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## DsKnees (Mar 4, 2021)

I figured I'd stop by and follow up.

I chose the ShopSabre 23. It is big enough, but only just. The weakest point is the limited Z height of 6". I can make do, but I'm right at the limit. 

There are other options that offer up to 12" gantry clearance, but I was a little scared they wouldn't be very stable. Like the "Industrial CNC" brand claims 12", but I got first hand advice that their machines don't cut very well, and apparently the guy has changed his company name and website a couple times.

I decided to trust that ShopSabre made the right compromises in the machine. They seem like a good group of people, their machines have a lot of add ons and accessories to increase the machine's capability, and they are less than 1 hr away from me. American made is an advantage for a major purchase like this.

For actual capacity of the ShopSabre 23, it is a 30x40" bed, 5" gantry height, and 6" Z clearance. In practical terms, I have found that the machine is capable of of milling down 2" depth into a 3" blank (without a spoil board). With a 4" overall length bit, slid into the spindle as far as it can go, I have a .250" z clearance over the top of the 3" block. It is enough, even if just barely. 



I did have a problem with the machine, but the problem was quickly and immediately addressed. So I can say their customer service is excellent. And being locally made really helped.

The issue is still confusing to me. I don't know if they would consider my machine to be defective, or if my expectations are just different from other customers? I don't know. I asked a couple people about the tolerances, and either they don't know or they aren't willing to say. 

The issue was the x axis rails had a slight convex curve to them across the width of the machine, which resulted in a slightly curved bed. I estimated it was around .030" over the 30" width of the bed.

This is an issue for me, because I need to be able to face off a rigid block of material to make it as close to perfectly flat as possible. And .001" off per 1 inch is a huge amount in machining terms!

But it may not be an issue to other customers. Most sheet material would easily bend that much, so the machine would cut equal thickness across the sheet. 

Like I said, they took care of it. I took the machine back (I'm less than 1 hour away), and they ended up transferring my electronics to a new chassis, and I had it back in 1.5 days.

I am surprised about how quickly they took care of it. And now it is cutting perfectly flat as far as I can tell. 

The moral of the story is it's a solidly built machine, and their support is excellent. However, if you are looking for a machine to do 3D work like mold making and machining rigid materials, it may be worth emphasizing that you need it to cut flat. Like actually flat. Just in case.


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## marecat3 (Nov 30, 2010)

Welcome to the forum


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## John Smith_ (Jan 10, 2020)

no input on the machine itself:
but, I have a friend that uses High Density Urethane (HDU) for pattern making.
it comes in 4x8 sheets and multiple thicknesses also in several densities.
I have used 15-20 pound density for patternmaking with good results and my friend uses 30 pound.
free samples are available from several of the Sign Foam manufacturers.
(much lighter than MDF or HDF in large projects. (but the dusty mess is the same).
(just an option to consider once you get up and running).


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## DsKnees (Mar 4, 2021)

John Smith_ said:


> no input on the machine itself:
> but, I have a friend that uses High Density Urethane (HDU) for pattern making.
> it comes in 4x8 sheets and multiple thicknesses also in several densities.
> I have used 15-20 pound density for patternmaking with good results and my friend uses 30 pound.
> ...


Thanks. I will look into that. I have briefly looked into "tooling board" products that are urethane based. They are probably similar? 

The MDF is ok for now. It's cheaper, but more time consuming. If I was on the clock, the MDF would cost quite a bit more in time than it saves in material cost. But I've got lots of time!

I was quoted ~$300 for a 20"x60"x2" sheet of tooling board, which works out to be $45 per mold I'm making. That's really not very expensive considering what I am doing, except in the last 1.5 weeks I would have chewed through atleast $600 of the stuff, all of which would end up being scrapped as I learn and make improvements. 

The suggestion I got specific to mold making was to shoot for 35-40# material. What I found comes in 20x60" sheets, and a variety of thicknesses. The denser material is recommended because it is easier to finish and use for fiberglass work. The reasoning is that I have to apply a sealer to the foam, and with the lower density foams, the sealer coat will be harder than the foam. So if I sand through the sealer, it becomes difficult to repair.


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## John Smith_ (Jan 10, 2020)

DsKnees said:


> The reasoning is that I have to apply a sealer to the foam, and with the lower density foams, the sealer coat will be harder than the foam. So if I sand through the sealer, it becomes difficult to repair.


yes, exactly. the lower the density, the larger the "bubbles and voids" will be that will hold and trap more of the sealer.
when I first started working with HDU, I didn't have a mentor or anyone to consult with about the processing.
through trial and error, I developed a system that worked for me and took notes as I tried different methods.
after a few years of that and perfecting my skills, I traveled around the country to other sign shops giving instructions (for a fee, of course) on how to work with and achieve the best results with HDU.
experimenting with new materials can be costly - but, education and experience is not always free.
looking forward to following your projects.


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## DsKnees (Mar 4, 2021)

John Smith_ said:


> yes, exactly. the lower the density, the larger the "bubbles and voids" will be that will hold and trap more of the sealer.
> when I first started working with HDU, I didn't have a mentor or anyone to consult with about the processing.
> through trial and error, I developed a system that worked for me and took notes as I tried different methods.
> after a few years of that and perfecting my skills, I traveled around the country to other sign shops giving instructions (for a fee, of course) on how to work with and achieve the best results with HDU.
> ...


Thanks for your comments. Yes, it does feel a bit like I'm on my own, but the thought that what I'm doing is similar to sign making instantly doubles the knowledge base I can look to! 

For experimentation, I just ordered some (cheap) automotive urethane clear coat. 

I've struggled to find an appropriate coating. Last I tried a pre-catalyzed laquor. It is easy to work with, but feels a bit rubbery when cured. Hardware store "automotive" paints and fillers are a disaster for my use.

The product recommended in the composites industry is from Duratec, but it is thick like a gel coat, and is applied in a ~20 mil (.020") layer. (Up to 50mil wet on wet.) That would destroy my tolerances! 

After ordering the automotive clear, I discover the composites store I visited a few days ago completely failed to mention that they also sell a thin urethane clear coat (Duratec) designed for my exact application... Doh! I thought I specifically asked about that type of product?

So yeah, I completely agree about experimentation and the struggle to find the right products and methods. It's expensive, but there isn't any way to avoid it. I'm sure that hiring you to share your knowledge was totally worth it to those shops.

I do have another project in mind, and I'm thinking it would be smart to take a step back and work on an "easy" project while I work through the techniques. Idea is a laptop keyboard holder designed for Apple's magic keyboard and magic trackpad. It holds both in roughly the configuration as found on a laptop computer. I have a crude prototype, which allows me to display my computer screen on my 4k tv, while having the familiar keyboard and trackpad layout on my lap.

It will be made in carbon fiber, because of course it needs to be carbon!


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## John Smith_ (Jan 10, 2020)

Dees - you are way further into the 21st Century than I am !! (gadget wise).
but the method of making molds and castings haven't changed all that much in 50 years.
certainly, the choice of products have leapt into the stratosphere but the craftsmanship is basic.
are you going to make just one of these items or are you going to set up for multiple castings ?

and a note about the hand-held gadgets: I am assuming that that you know these things "can" change in size and configuration with every upgrade ? so what you make for this year's products may not fit next year's edition.
looking forward to following your journey


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## John Smith_ (Jan 10, 2020)

and a note for after the modeling is done in a porous material such as HDU and other foam composites. (not MDF, HDF or other fiber type material).
a lot of my colleagues had problems with primer and paint adhesion. (6 months, their paint job just peeled off).
the method I discovered was after all the the mechanical work is done, take the product outside and hit with the high pressure water hose (NOT power wash) and you will see the dust blown out of the surface. very dramatic change in color when you do this. it dries in the sun in a short time - so don't worry about the foam being waterlogged.
try that on your sample pieces first to see if it improves the finish on the material you are actually using.
primers and sealers do not stick well to surfaces that are "dusty".


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## DsKnees (Mar 4, 2021)

Alright, update time. My machine was supposed to be fixed, but it turns out it still had issues. 

The original issue was the rails across the gantry for the x axis. Those were much improved, although not quite perfect. The new issue I discovered was a curve in the y axis rails. 

First off, I could see a variation in the surface finish of the phenolic top from one end to the other. One half felt smoother than the other. And I could see further evidence of a problem when I attempted to continue my "reference surface" project. I quickly discovered that if I made a pass and then rotated the workplace 180 degrees for a second pass, there were significant high and low spots that revealed themselves.

To figure out what was going on, purchased some new equipment. It was an expense I was trying to avoid, but I suppose I can't expect precision if I don't even have the tools to measure if something is flat. So I purchased a 36" Starret precision ground straight edge, Mitutoyo feeler gauges, calipers, and a few other things that are good to have, but not strictly necessary for this particular project.

To measure and identify where the problem was, I placed a straight edge on the rail, and I measured the gap between the straight edge and the rail with feeler gauges. (I used a t-slot clamp in the middle of the table, but with almost no pressure--just enough to hold the level in place.)

I found the maximum gap was .015" at one of the front corners, and .018" on the other side. 

I was surprised to find that when I loosened the bolts on the rails, they snapped into place by themselves! I only loosened the bolts in the problem areas, leaving the rest fastened tightly. So it ended up being fairly simple to fix.












It is clearly better now. I can see an improvement in the consistency of the surface finish from before. I do not know if the rails are parallel, because I have no way to measure that.


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