Simons router

[simon78++]

Hi All!

I am planning to build a CNC router machine. I have a couple of THK SR15 rails as well as an THK KR3310 actuator as Z-axis. I am planning to build the frame of 50x50mm square steel pipes (don't know if thats the correct name, but you get it). The X-rails will be mounted quite high so that I don't need "legs" for the portal. The Z-axis is quite short ~85mm or so. I was planning to build the portal out of aluminum, but my local "metal shop" did not carry that dimensions in aluminum, only steel. So, im now thinking of building the portal of steel as well. The thing that concerns me is that the portal might be quite heavy, and hence takes a lot of force to accelerate. And, as my steppers are quite small, the portal (X) axis might be very slow.

As i do not have any advanced tools, just a little more that "standard garage tools", i am spending a lot of time to think how i will build this thing with the tools available.

Any comments are more that welcome!

Blue: steel, grey: aluminum and brown: MDF.

[Oldmanandhistoy]

Hi Simon,

All looks very well designed to me.

Portal = Gantry?

From one of your pic’s it looks like a stepper motor in the centre of the X axis but it also looks like you have two screws to drive your X.
Just taken another look at the pic seems you will be using belt drive for the X; will the screws be ball screws?

If you’re concerned about having enough power to move your gantry you could always use two steppers instead of the one.

I say build as you have it and if there are problems then look at the two steppers.

What do you plan to cut with this machine?

John

[Haydn]

Hi Simon,

Looks good to me. From the title of your jpegs I assume you intend using a dremel for the spindle? If you are using a dremel you may get away with a smaller aluminium section on the gantry. I built my machine out of steel section with limited tools. I used steel epoxy in all the joints and bolted them to get a perfect mating surface - stress free and no welding distortion to contend with. Takes longer to build than it would in aluminium extrusion but steel is cheaper and stiffer. What rating are the steppers you have?

[Oldmanandhistoy]

Hi again,

I hope the main intended spindle is not going to be a Dermel it would be a waste of all those lovely linear slides.

Hayden how long and how much have you been using your machine? I would like to build a steel machine but have no welding skills so am very interested in that steel epoxy.

John

[Haydn]

Hi John,

My machine is in its final stages, hope to be finished by xmas. Just have to fit x ballscrew and motors. The steel epoxy is a god send for me as I dont have access to a mill etc (im a guitar maker). I found a friendly engineer who had an 8'x4' surface table. I covered it in cling film and basically set my steel sections in epoxy on the cling. This is how I did my rail mounts for x and y. They are very accurate (the epoxy doesnt contract as it sets). It avoids machining (if you machine one side of a steel section you need to machine the other or it will deflect), and the problem of frame creep/deflection from welding (unless you have a large oven to destress it). I hope to put up a thread some time of some of my build.

For now if you want to see where I got many of my ideas from have a look at

http://oneoceankayaks.com/madvac/madvac_index.htm

[simon78++]

I guess portal==gantry. The name of the machine was drummeln, after the spindle i used as a prototype, and it kind of stuck. Now i am planning to usa an el cheapo 850W spindle. I am using one small stepper for the X-axis, using a "timing belt" to drive both two threaded rods.

[simon78++]

Forgot some things...
The steppers are quite small i guess (58mm in diameter 2.6V and 1.9A). I don't know if they are strong enough. But if i understand it correctly, the torque decreases linearly with the speed, so, if they are to weak, I will only decrease the speed.

I am not sure what materials I will be able to cut with this thing. I am primarily planning to cut aluminum, wood and plastic. However, I try to design it as robust as possible with the material available.

Do you think its possible to weld the frame together, or will it not be accurate enough? I don't know what kind of accuracy thats required.

I'm thinking of moving the Y-rails to the top and the bottom of the gantry. This will shorten the distance between the router and the gantry by about 40mm (from ~90mm to ~50mm), reducing torque around the "gantry axis". This require that I move The gantry up 30-40mm or so to make room for the lower rail.

PS. Drummeln means an oaf or a jerk in Swedish.

[Oldmanandhistoy]

I think those stepper will depend on the drives you have. How many wires have they got?
Speed for cutting timber needs to be at least reasonable or you are just going to burn your cutters to death.
If you can run the steppers bipolar parallel and at 3.5A and have plenty of Volts you may be ok. If you are planning to cut mainly timber then go for speed over power; you can always take lighter cuts.

John

[Oldmanandhistoy]

As for moving the rails on the Y axis imho the axis is going to be ridged enough as is and you are just going to move the flex from one place to another.

John

[simon78++]

I will drive the steppers with around 2A and up to 35V (chopper drive). The steppers are bipolar. I am using a Allegro A3977SLP based board.

[Oldmanandhistoy]

You may be ok do you have the holding torque rating + torque curve details?

Are you using ball screws or trapezoidal/acme screws and do you know what pitch/tpi they will be?

John

[simon78++]

I am ashamed to say it, but i will use ordinary M8 threaded rods to start with (Have spent to much money on the linear bearings). Of course I will try to upgrade this in the future. So, a M8 has 1.25mm/turn i think. I have no data on these steppers. I bought them used.