Desktop CNC router for plastic molds?

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#21

We got one of these [shop sabres

this link says starts at $15k… Pretty nice machine. Nothing super fancy, just a basic 3 axis but has a nice spindle on it. Mostly I just cut core with it.

I like your idea of making the frame out of carbon… I’ve been thinking about this as well for some while. I have so much scrap carbon I could easily build out several machines a year from carbon. I’m thinking I should probably start making a carbon fiber 3d printer chassis first, cause it’s a bit smaller. There was some other group that was working on one but, never saw it make it to KS… maybe they couldn’t make it cheaply enough?

Do you have your chassis design nailed down? What molds would you use for those parts? You plan on making it so it assembles from pieces or one big monolithic frame?

Sounds like fun!](http://www.shopsabre.com/cnc/router/rc-series/)

#22

I’m hoping that won’t be the case with what I’m building. I’ve bought chunky THK rails, half inch ball screws and my gantry is steel reinforced carbon fiber. I’m not sure how I could make it more rigid…

How is a lack of rigidity effecting what you are doing?

#23

I would use the 2.2kw without a doubt, but just make sure the gantry is stiff enough to carry the 11 pound motor without any vibration or deflection problems. When it comes to routers, mills and other machine tools- mass rules. If you have deflection problems, the first symptom you will notice is chatter on your cuts.

#24

I get deflection problems with my manual router when I try to use an overly large diameter router bit on a hard material or when I try to make cuts that are too deep for a single pass.

I guess some of it will come down to how the job is set up and the choice of router bit.

There is also the issue of choosing the right spindle for the material being cut, as you said. I am a little worried about this part because I don’t have enough in my budget to buy a quality 2.2kw spindle with all the trimmings. I would be looking for a bargain on one of the cheaper Chinese ones off eBay.

I haven’t researched this topic fully yet but for every other electronic component, the advice always seems to be to avoid the cheap Chinese one if you expect to make anything you could sell and have it ready while you are still alive.

As I already have a 2hp manual router, I will try using it when I get everything else up and running. If it does what I need then great. If it doesn’t work well enough, then I’ll start shopping for a dedicated CNC spindle.

I am starting to lean more towards a fixed gantry machine design to make the thing more stable.

#25

I miss read as using 20mm extrusions not rails. Lack of rigidity mostly just limits speeds by limiting accelerations. You just need to find the compromise between finish quality and time.

#26

There is a company selling large commercial CNC routers with carbon fiber gantry bridges. I believe they mill them instead of using molds.

I have been experimenting with making my gantry plates using two optically flat mirrors as my molds. I sandwich the cf between the two mirrors under heat and pressure for curing. The plates come out as flat as I have seen.

Once I have assembled a complete gantry, I want to use it to create a mold and then make the whole gantry as a single piece so I don’t have to worry about the strength in the joints with screws in carbon fiber.

I am using non-woven recycled random matrix cf fabric for a core material for the plates to add additional thickness and rigidity. That along with woven fabric should provide plenty of strength.

In addition, I plan to try a slightly more trade gantry using aluminum rectangular tubing wrapped in carbon fiber to see which I prefer.

I tested some of the cheap building materials from Open Builds part store and I was very disappointed with the quality. I could literally bend and break their L blacks and corner connectors with my fingers. It seems like you have to make everything yourself if you don’t want garbage and you don’t want to spend a fortune…

#27

What part of CA are you from? I’m from sac, we have a maker space here but the staff there are very rude. I’ve only been there 2 times, each time was a different person but they were both rude.

#28

I’m not from CA. I live in NY.

There are a bunch of maker spaces near where I live. Some are better and more suitable than others though. There is one in particular that looks promising as it has high end CNC mills, lathes and routers as well as a lot of manual machines. They also offer beginners classes so people like me won’t accidentally chop their hands off.

It sucks that the staff were rude at your local maker space. I can see them being a fairly intimidating environment for new comers so the last thing you want is staff who don’t help and make you feel welcome. It goes against the whole maker space ideology imo. They are meant to be creative and collaborative environments that foster a sense of comradery between like-minded entrepreneurs. Nobody wants to spend any time in a room full of unfriendly people…

I found a few people who live near me on that cnczone forum and one guy kindly offered to show me his machine, teach me how it works and machine a mold for me so I can see the level of quality that is achievable.

I bet that, if you asked, you would find people there who live near you too and probably some people who would be happy to help you out. It might work out better (and cheaper) than a maker space.

#29

This is not a real recommendation at all because I haven’t bought one myself, but like some of you guys I am looking into this, too.
If one doesn’t want to build, then the Chinese machines from Omio seem to be one worthwhile step up from the bulk of the Ebay offerings.
What I read online over the past few months is that many Chinese machines need to have their drivers swapped pretty much right away and they suffer from various other ailings. Supposedly the controller box of the Omios is good and stable. Also, their better models use linear bearings which are stiffer than the rod ones used on all the other Ebay offering.
It does seem Omio suffer at least one or two of the “Chinese deceases” like not having shielded cables and after sales service can be a bit hit or miss. But overall, a lot of end users seem to be happy with spending a little bit extra on this brand, though I think I have seen 1-2 guys complain about getting a lemon. No matter what, they are probably stiffer than any of the more branded and popular “US” routers.

If you are interested head over to CNCZONE and look through this long thread on them which by far is the best source of info I have found on these machinese : http://www.cnczone.com/forums/chinese-machines/275124-cnc-cad-software-forum.html

As I said, I am just passing on what I have found myself looking into this exact subject. This is not more than that.

#30

To give something from my experience .
I currently own a 8 000 euro class machine . There are better out there and there are worse . I started to look at the internet at forums like cnc zone etc and i was ready to buy a 1000 euro cnc from ebay. Yes those Chinese ones. Then i wanted a little bit more space of work and i went a little higher …then i wanted some extra rigidity and i went a ittle higher and i stopped there. Now after some time with the machine i can give you some hints .

If you want the machine to operate and you worry for the noise try the water cooled selections of router . The air cooled tend to make more noise.

If you want to be able to cut aluminium - like me , for molds of prepreg you should look for a rigid machine made of steel and aluminium . So dont expect a cnc made of plywood and aluminium to do the job. The passes will be very shallow the outcome will be not good .

Get a cnc with inverter so that you can adjust the spindle as an operator from your computer as it is far more convenient, you see the result and you adjust in real time .

Dont expect that you will get a cnc , in 2 days you will have it ready and by Monday you will start Cutting . It will take a LOT of time wasted in order to see a smile at your face . - Given the time that you give daily etc.

By the way i see it is that you should pay as much money as you are able to in order to save time that would otherwise have to spend with no support of Chinese systems and endless ours in forums were you will seek for advise etc etc . Because Cnc is not just a tool , it is another world .

So Yes Buy a cnc , the best you can . It is the best upgrade you can have at your workshop . And it makes you autonomous . But dont think it will be an easy trip to get there

#31

I couldn’t find any low cost / high quality ready made CNC routers. The feedback on most / all of the $500 - $2500 ready made Chinese CNC routers was that some were just about ok for hobby work on soft materials but not for anything close to professional work.

Most sounded like more trouble than they were worth to me. People complained that they came with pirated software, underpowered spindles, poor build quality, too much assembling required with poorly written instructions and they kept stopping half way through a job etc. In short, none of them seemed particularly cheap when compared to what you can build yourself for the same or less cash.

I am still building mine but… so far… I have spent $1500 for almost everything I need and when finished, I will have a solid machine with a steel / carbon fiber frame, good THK rails, a carbon fiber and aluminum gantry with 30" + of cutting space and run on properly cooled Gecko g540 with low inductance Nema 23 motors + high quality 2-start lead screws.

Mine won’t be the best machine in the world (or even close) but there was nothing available ready made with comparable parts for less than $6000. There are no “cheap” desktop machines with good square rails and lead screws etc.

I have been getting a lot of help from some very generous people on various forums so I feel good about what I chose to do. It’s not super easy but it seems well within what’s possible for a patient diy fan.

I take the point about expecting a frustrating learning curve. I am hoping that the help I am getting from some experienced builders will cut that down a little though.

#32

Hi Zebra,
Do you happen to have a build log on one of those forums?
Perhaps you can get some inspiration, if you haven’t already come across it, from this one:
www.mycncuk.com/threads/10658-El-Beast-Initial-design-phase-comments-and-critique-welcomed!/
(first pics are of his Chinese OMIO, but the thread is about him building a bigger and better version)

#33

Not sure I would call it a build log but I have a thread on CNC Zone where people have been helping me as I go through the process. Those guys helped me dodge a number of bullets and school-boy errors.

I have committed to posting some info on my build when I am done as some people there have an interest in seeing how I use carbon fiber for my gantry. Given how much people have helped me, sharing is the least I can do (assuming I end up with something worth sharing).

I am not copying any existing designs for my gantry as I haven’t seen any diy Builds that use CF. I’m not planning on reinventing the wheel or anything but I do want to design the part for the material I am working with. Specifically, I want my gantry bridge and side supports to be all one piece to minimize the need for using screws to join cf parts together.

It’s a fun project!

#34

Sounds great and as you say, there are some helpful people on those forums, like here. Also, I think now, there is quite a consensus on which basic designs work (low as possibly gantry, linear HIWIN rails, etc) to increase rigidity in routers (as opposed to mills). You will still have the odd guy come in and say, you need a +1 ton machine with a metal frame, but for alu molds, you actually don’t;-).

Please do share a link to CNCzone once you feel like it, would be cool to see your thoughts, the input you got and the result.

#35

Here’s a pic from the Marine Concepts web site. From what I understand, the router pictured wasn’t stiff enough from the mfg so they added the carbon structure you can see attached to the top of the gantry. This might be useful to you as you build your machine.

Or it could be just an interesting side note. :smiley:

#36

To be honest i dont understand the use of carbon carbon on the machine. The link you provided is a gantry bridge where the span of the tool is about 8 meters and is problematic causing flexion to the tool . For a steel I beam 220 for example they would may have 15 mm of deflection at the midle… thats why they do it. But this in not the case with your machine. Get a steel or 2000 alloy piece of metal and you will be fine

#37

If you Google the terms “carbon fiber CNC gantry” and “carbon fiber gantry beam”, you’ll find 2 companies that offer a carbon fiber CNC machine products.

One seems to sell custom CNC routers with a milled carbon fiber gantry and other milled cf parts. I’m not sold on this approach at all. Milling solid blocks of cf for parts that big seems wasteful and sub-optimal but I’m not 100% sure on this view…

The other is a custom carbon fiber parts business that makes and sells custom carbon fiber beams for use as gantry bridges and other machine parts. They look quite good.

The latter appears to use some kind of compressed cf reinforced polymer. Neither use woven cf laid in molds like most of us use here.

Using a sheet molding compound for cf CNC components makes sense to me for this purpose as it offers greater multi-directional rigidity, is cheaper to manufacturer in larger volumes and easier to mold into complex shapes. With that being said, I am not sure the multi-directional rigidity is needed for this purpose as it seems like the parts would be under stress from 3-5 predicable directions (as the router moves on rails).

I am making my cf parts in traditional molds but I am using a mix of regular woven cf fabric, bi and tri-axial fabric, random matrix carbon fibers (made into a sheet molding compound) and carbon nanotubes mixed into the resin for some of the layers.

For my cf gantry bridge, I am using a rectangular woven cf outer shell with a bunch of .75" carbon fiber tubes inside as reinforcements set in cf sheet molding compound. My plan is to use a double-bridge design. One regular gantry bridge to hold the Y and Z axis rails and a second bridge under the table connecting the bearings between the X-axis rails. I believe this square gantry design will offer greater rigidity than some of the traditional 3-sided gantry designs. We’ll see…

I am also adding some steel plates in select positions inside the cf gantry parts to hold the screws needed for my THK rails.

I think the design I am working on will provide the greatest rigidity possible without going over my budget but due to my lack of experience, I am not really sure exactly how much strength and righty I actually need. I am positive the design will offer significantly greater righty than any of the comparably priced desktop CNC routers on eBay or any of the diy kits available.

The aluminum build parts I initially ordered from Open Builds parts store were real garbage. I could literally bend their T and L brackets with my fingers. They went straight in the trash so the bar is relatively low…

#38

The part I remain most confused about (still) is choosing the right spindle. I have had plenty of advice. It’s just that nobody seems to agree. I am choosing between a 2.2kw CNC spindle off eBay, one of the lower speed milling heads from Little Machine shop or just starting off with using my Ridgid 2hp fixed base router to see how it goes.

There are convincing arguments for all spindle options…

Even though the Little Machine Shop milling heads offer less peak horse power and speed, they look a lot more robust than your average Chinese CNC spindle and they hold larger end mills (up to 5/8"). As I care more about accuracy than speed, I am wondering if these milling heads are best for making aluminum molds. Then again, maybe my machine won’t be rigid enough to use a low speed spindle effectively.

#39

This is the cf gantry beam maker btw:

http://www.cz.compotech.com/example_applications/example_applications/machine_building_components/gantry_beams

Looking at the pic, it seems like they also use filament winding to make cf parts.

#40

Not sure I read you correctly, but quick qeustion, are you using a regular router gantry design where the Z is mounted to the gantry or the, supposedly more rigid design where the whole gantry itself moves up and down and becomes the Y? The latter is way a around the problem of trying to increase Z clearance but still having a sturdy Z. In the regular design, if you want more Z clearance you build a taller gantry but that makes it less sturdy.
An increase in gantry height without a rigidity penalty might make sense as you could e.g. machine taller parts that you don’t need to make molds off of. Like some one-off plugs in foam, etc.

As for spindles, read up on spindle speeds and cutting aluminum. Going slower may not really be a good idea. I would think Little Machine Shop’s milling heads are for manual mills where the feed rate is not as high as you can get your CNC one to be?
Maybe a bit of info here, didn’t check that carefully: http://www.cnccookbook.com/CCCNCMillFeedsSpeedsBasics.htm
But if your router ends up being sturdy and fast enough you would probably want a fast spindle. Especially for alu molds as you could probably save a lot of machining time. I could be wrong on all this - you are further down this path than I am;-)