[svenw]

Hey, everyone, I am currently finishing up my first year of Mechatronics Engineering at the University of Waterloo in Canada. Our class has decided to host a design symposium in approximately 5 months so that everyone can show off there projects that they were working on during their co-op terms ( Waterloo Engineering students switch between school and co-op every term to get a good grasp of real engineering practices, this also leaves us with lots of free time, due to having a void of homework and studying).
I have decided to embark on designing and building a CNC router.
My main goals are:
- Keep it fairly cheap ~ $1500 initial investment including a router
- Ability to machine 1/4" aluminum and polycarbonate (I am also a mentor for a FIRST robotics team and I hope to accurately machine gearbox plates from plate aluminum)
- A cutting surface of 12" X 24"
- A small enclosed design so that I can keep it in my basement
- A good portion designed by myself / an old design modified to meet my needs

I started off buying the Momus design, because it appeared to fit my needs the most. I read through the plans and looked at ways I could modify it to meet the rest of my goals. This meant to remove most of the gantry and design it a bit more rigidly using a Joe's hybrid approach of aluminum extrusion, V bearings and angle iron. I also decided to use lead screws instead of the belts due to the increased accuracy for aluminum.

As this is my first CNC build / design, I am looking for help and advice regarding the design. I included 3 pictures of the rough design that I have so far. So if you see any issues or anything I can improve on, or if you have any questions about my design decisions please let me know


So far I have purchased
$20 - Momus Plans
$105 - 200 oz-in steppers (They are fairly weak but I am hoping to use them for now and in the future upgrade the one on my Y axis and put two of these on my X axis)
$25 - computer with parallel port

Well I hope this will be my first of many posts as I should be starting with the base as soon as my exams are over. Once I have free time I will also be asking more specific questions as right now I should be studying for my calc and statics exams

[OCNC]

Your modifications look good. I like the use of the Vee bearings on all axes and switching to threaded rod should give you better drive stiffness over timing belts for milling aluminum. Using Vee bearings greatly reduces component count and should improve the ease and possibly the accuracy of initial adjustment. I can't tell if your rails are square edge aluminum angle or true vee profile. If they're aluminum they can be 'conditioned' into a vee rail. For more on this process see page 14 of Chapter 1 in KRMX01 pdf.

Chris

[svenw]

I can't tell if your rails are square edge aluminum angle or true vee profile

Chris, the idea is to plain steel angle and to make a more pronounced V using an angle grinder.

I currently have 3 200 oz-in stepper motors (KL23H276-30-8A) I purchased these thinking they were 282 oz-in (which they are when wired in bipolar) Unfortunately I was planning on using them with a hobby CNC driver.
Are there any low cost bipolar drivers on the market? Or should I purchase a stronger 300 oz-in motor for the Y axis, and put two of the 200 oz-in guys on the X axis, Or will I be fine using just the current steppers?

Thanks,
Sven

[OCNC]

Chris, the idea is to plain steel angle and to make a more pronounced V using an angle grinder.

I currently have 3 200 oz-in stepper motors (KL23H276-30-8A) I purchased these thinking they were 282 oz-in (which they are when wired in bipolar) Unfortunately I was planning on using them with a hobby CNC driver.
Are there any low cost bipolar drivers on the market? Or should I purchase a stronger 300 oz-in motor for the Y axis, and put two of the 200 oz-in guys on the X axis, Or will I be fine using just the current steppers?

Thanks,
Sven

Are you saying that those steppers are weak because you've actually tested them and tried to stop the shaft from turning or are you imagining they're weak because they don't match up with the general trend of what you see people using?



In my opinion the best bipolar drives available in the DIY CNC world are Gecko's. If you're serious about staying involved with DIY CNC then they're a very good investment...but they do cost more than many others that are available.

Chris

[cb_designer]

You should be fine using those motors with the hobbycnc driver... I am using 127 oz. in motors with the same board on my machine for all 3 axis and they seem to be holding up to the task... They are what I had on hand and I wanted to test them before purchasing new ones... When I build my v2 machine, I will go with larger motors, but if I were you, I would go with what you have...

[svenw]

Are you saying that those steppers are weak because you've actually tested them and tried to stop the shaft from turning or are you imagining they're weak because they don't match up with the general trend of what you see people using?



In my opinion the best bipolar drives available in the DIY CNC world are Gecko's. If you're serious about staying involved with DIY CNC then they're a very good investment...but they do cost more than many others that are available.

Chris

Yes, I am worried about them being too weak because of the general trend of what people have been using. And although the gecko drive are most likely the best bi-polar drives out there, they are unfortunately too far out of my budget. Instead I am looking for something around the cost of the Hobby CNC, if not I will most likely be going with the Hobby Pro kit.

You should be fine using those motors with the hobbycnc driver... I am using 127 oz. in motors with the same board on my machine for all 3 axis and they seem to be holding up to the task... They are what I had on hand and I wanted to test them before purchasing new ones... When I build my v2 machine, I will go with larger motors, but if I were you, I would go with what you have...

I think I will be staying with what I have, worst case scenario I will have everything together and realize they are too weak and just buy some larger ones.


Since I finally finished school for the summer I had some free time at home. I found a great torodial transformer which I pulled out of a 15 amp Farm charger. I measured the various voltage possibilities which varied from ~8 to 14 VAC.
Since there appear to be 6 separate loops in the secondary windings, would I be able to run half of them in series, creating essentially 3 loops twice as long? If my understanding is correct this should double my voltage giving me a possibility of 16-28 VAC which will be perfect for a Hobby CNC power supply.

I also started and finished the main box. I asked a good friend of mine who does some awesome cabinetry and some unique furniture if he would be willing to help me out. We started yesterday morning and picked up 2 sheets of maple veneer plywood. 16 hours later we had cut, glued, sanded, and finished a solid base for the router.

This project is turning out to be a perfect experience and I already have so many design improvements which I need to put into solidworks

If anyone knows their way around transformers I would love to have some advice about how to modify the torodial I found.

Let me know what you guys think so far, and and stay tuned I will most likely be starting with the electronics and Gantry in the next 2 weeks.

-Sven

[vtxstar]

You have access to an excellent commercial table saw and the results of your woodworking reflect carefull cutting and planning. Very good!

Regarding your transformer... confirm that the pairs of output windings are not connected to other pairs and if so, they *probably* can be 'added' to achieve the voltage you are looking for. Rectification and regulation will follow unless your driver board(s) and electronics can receive AC input.

I suspect it is too much to ask if you happened upon a schematic of the farm charger while salvaging the transformer?? It may be possible that the wiring pairs are maked.. perhaps one with a 'dot'. This would indicate which wire has a phasing relationship with the input mains AC.

Also check other builds using toroids for similar situations. Someone is certain to have tried/done this before.

Again, nice work!

-=Doug

[krams976]

I currently have access to a wood cutting cnc and would like to know if anyone has put the pdf files for cutting into vecters. just to maybe let me look adjust and maybe save some time. Would be helpful and id apreciate it.