[vakeiros]

Your project looks awesome. I'm glad more people are deciding to go the epoxy granite route, and build their own machines.

You are a bit ahead of me in that you reached out to people here on the zone for some feedback, but I've began on a project quite similar to yours with a PM-940M milling machine.

I intend to use the castings from a PM-940M milling machine and convert the machine to linear rail CNC. I've done quite a bit of work designing my vision and spot some similarities to yours.

I too intend to do epoxy granite but I'm going to epoxy granite around my original cast iron castings to increase the weight and rigidity. My machine as built weighs around 1000 pounds or 450kg, but with the epoxy, I will want to get in the region of 1500 pounds or 680kg. I wanted to put sheet metal steel on the outside of the epoxy castings to add in rigidity, and like you specified place bars in areas that can be machined after for alignment. The machines look similar in design, but I suppose that's not too much of a surprise being a traditional VMC. I'll have to double check my travel dimensions, but yours look very close to the travels I expect to achieve as well.

I will be using an air cylinder as well for my Z axis counterweight. I saw a post here on CNCZone about someone using one and balancing the pressure in the cylinder and using an air receiver and decided it was a brilliant idea and was going to follow suite.

I planned on using 25mm linear rails all around and 2005 ballscrews on all axis being I was using the air cylinder and balancing out the weight. I intend to use 750w servo motors on the X & Y but wanted a 1kw on the Z axis (not sure if that's necessary with the air cylinder counterweight though). I purchased an iso30 spindle which I'm told has the same taper as BT30 but doesn't allow for a pull stud, so I will have to replace the drawbar to make it work. I want to go with a 3.7kW AC servo motor to drive the BT30 spindle but am having trouble finding out where to get one because I want at least 8000rpm, and if I can a 1:1 drive ratio so I don't loose any torque.

For my control system, I really wanted to go with a Centroid Oak, but the price is so high, although I do understand it's a really good controller. I decided instead to go with linuxCNC, as it will teach me something new and be a good experience all around. With linuxCNC your able to use linear encoders (which I intend to install on my three axis) to ensure you have absolute positioning. I like the chineese controller you posted but I'm a bit timid in the after sales support, especially for something I will be completely relying on.

I see one of the things your doing is going for a epoxy granite table. While that can be done, I worry about flatness with the granite table and holding stuff down to the table, even though you said you will put threaded inserts. My plan to counter this is get a piece of 2" thick by 12" wide by 24" long steel and bolt it to my Y axis saddle, then machine it flat once everything is square on the machine. I also am planning to do a grid T-slot pattern like some of the Haas VMC's.

Another suggestion I have is your Y axis saddle, again that can be done in epoxy granite but what I'm doing is taking my T-slot table from the milling machine and turning it upside down, and installing linear rails on the ways. You can easily find 9"x42" Bridgeport tables on eBay, and this may suffice as your Y axis saddle.

I hope I didn't ramble on too much and some of my similarities and differences help you with your project. I hope you don't mind but I've posted some pictures so you can see my design, and included a picture of of my 3d printed PM-940M linear rail CNC with epoxy granite retrofit.

yeah you make a fair point in using same 2005 screw in Z axis since it's counter-balanced but I decided to go bigger anyway.

well about the controller I think I'm giving it a try, it looks very nice and they've been very supportive, sent me all the doccumentations and everything I asked for. I'll be buying the servos also from them and I'll go with an absolute servo/controller system.
I've been working with mach3 since my very first machine, I don't have many complains about it except with my current machine if I stop a program when it's running most of time when either I restart the program or load a new one the machine will be full of jerking micropausing between program lines, have to restart mach3 so it goes nice again. it's kind of stupid, I'll have to probe the work again and so... PAIN!!!! thought about linux cnc but I really like the idea of the dedicated controller...

about the table, like i said before here in Portugal I have serious problems getting steel stuff at fair prices, so I'm making it this way, I'll cast the table with EG and leave a thin layer of epoxy at the top so I can cut it flat with the machine itself after its fully assembled and all squared.
the steel inserts will be the for threading and probably 2 or 4 with reamed holes for position pins so I can place an aluminum top with some grid holes with threads and position holes.

same goes with the saddle.

about your similarities and pictures no problem at all, almost every VMC have the same look and if it works why try to re-invent the wheel? so please share with us your project. I really like this forum because of all the sharing so we can learn with each other.

anyway thanks for your input