First CNC machine

[kev]

Hi Kev.

just 1 observation. Are you only using one rail on the y axis? if so then the 250mm travel + the distance to the rail + the length of the cutting tool will put quite a bit of force on it!

Good luck with the build.

hi, no i was thinking of using one rail on the top and one one of the bottom, tho im going to redesign the z axis so that the motor is not so high up, possibly mount it on the other side of the alu profile, offset the weight a bit. im also thinking of keeping the linear bearings fixed and letting the rails move up and down on the z axis instead, this should keep 250mm of 12mm aluminium sheet fairly rigid.

Its hard designing things , might just order lots of bits and make it up as i go haha

[Ross77]

Sorry didnt notice the label tag was dog legged through the lower one.

Good idea to fix the blocks and let the rails move up and down on the z axis. Are they 4 way equal loading? Thats how I'm going to do it on mine. I would allow for a least a 1/3 of the rail to be held in the blocks. So for a 250mm travel you would need 375mm rails.

If its just for sign making then do you need so much travel? Why dont you just use the stand idea but have different size collars to rise it up in increments. Some people have also used multiple mounting heights on the z axis plate to allow for the cutting tool, might be worth looking at.

Its hard designing things , might just order lots of bits and make it up as i go haha

Yes but isnt that the fun part.

[kev]

Sorry didnt notice the label tag was dog legged through the lower one.

Good idea to fix the blocks and let the rails move up and down on the z axis. Are they 4 way equal loading? Thats how I'm going to do it on mine. I would allow for a least a 1/3 of the rail to be held in the blocks. So for a 250mm travel you would need 375mm rails.

If its just for sign making then do you need so much travel? Why dont you just use the stand idea but have different size collars to rise it up in increments. Some people have also used multiple mounting heights on the z axis plate to allow for the cutting tool, might be worth looking at.


Yes but isnt that the fun part.

Yes i think the bearings are 4 way equal loading, they are adjustable as well, theres a close up picture of one in my gallery.

It is supposed to be for sign making and would actually only require about 10mm of z travel but i want to cut big things inside of it lol, i might not go for 250mm of z travel i think i will test it first, see how much flex there is.

I have ordered some 45x45mm box section and some more rails so i think i might try the make it up approach until i come up with some good ideas.

[Ross77]

I know what you mean about just making it up, its so much easier when its there in front of you, than sitting at a computer with CAD. Have you seen the design guide for the blocks? looks like you will have to be careful with the spacing as any racking will cause them to bind.

Since they are 4 way loading have you considered putting the x axis rails on their side, that way you just need a flat plate to bolt the carrages to the y axis rail.

Where do you get the ali sections from?

[kev]

Yea i have seen there website, i think you are suppossed to use one block without the side bearings, hopefully it should work ok though.

I have thought about putting the rails on the side but then there will only be one contact patch per block instead of 2, but putting them on the side would give me a bigger y axis. il see how it goes.

the alu profile is from RS

[kev]

quick update,

i have put the rails on the side, and its made everything alot easier,
i have made a design on autocad and started to roughly make it out of steel, as you can see not many holes line up lol.

im currently waiting for some 45x45 alu profile and the plan is to have two vertical sections bolted onto the alu side plates then, two long pieces across forming the y axis. im also planning on mounting the y axis motor on the inside and using a pulley to attach to the screw that will go down the middle of the y axis.

[Ross77]

Looking good. with regard to the rails being on their side with only one contact then in dosnt matter as in reallity you are only supporting the weight of the y and z axis. The plunge of the z axis will counter some this and you will then have max strength (4 contacts) in the sideways movement of the x axis where you need it to counter the cutting forces.

Not sure it I would have moved the y axis rails as well tho. For that long travel on the z you need them as far appart as poss to reduce the moment, the other side effect is that the y rail has moved the spindle futher way! You might want to shift the y axis rail back a bit further to compensate, dosnt mater if the motor overhangs a bit. mind it would be easy the remake the side plates later if it dose cause any problems. (Chatter, binding etc.)

Did you find RS the cheapest for the aluminium sections?