First time build - Steel Frame CNC Router

[Boyan Silyavski]

Hi, a bit of advice.

I see sth strange in this machine. May be i am wrong, but before buying and spending and cutting material, better do a continuity check. Element by element the way you will mount it together and check if thats possible and the difficulties.
I do that with whatever i build and in spite of that some times is difficult in real life to mount things together, there was an element in my first machine that cleared mere 1-2mm or it would not enter. Even that i have checked that 10 times .So dont use just copy paste, Hi but move the elements as they will be moved in real life.

My rule of a thumb is to leave clearance holes at least 1.5mm bigger in diameter, better 2mm. Cause the paint, the welding, etc... And when you weld, aim at precision, dont be in a rush. I have welded 1 meter machine under 1mm precision and 3 meter machine around 1mm. Its not a joke. And it was one of the first thing i welded. By the way 250A mig is best for home fabrication and costs about 350euro on ebay. Later when you can could change gun and cable with a brand one. Thats what i did.

Buy more material and use extra cut to size pieces as hard stops so you could achieve precision mounting. later you would use them for sth. And steel is cheap.

You need light preload, not 0 preload for the bearing blocks. Wider block serve nothing more than easier to mount usually for the gantry legs. On Z almost always the normal blocks are a must. Make sure you buy the long carriages.

[examorph]

Hi Boyan, thanks for the advise. I looked at the design again and the main areas I think may cause me some headache are lining up the x axis bearing supports with the gantry sides (as clearances are small) so guess there will be a lot of back and forth with the hand file for this, and another area was the ball screw bearing support depths on the x axis being difficult to line up without a mill, so I reduced these in width and made them into spacers with thru holes instead (nut/bolt onto box section), allowing me to again skim them down easily with a file if required.

Also, I noticed that I could extend the rails on the x axis all the way along the box section and reduce the length of box section to better utilize the full length of the ball screw, so the X axis rail is now 1050mm. Front hard stop was easily added with a bit of 50 x 50 box section but for the back, I used 10mm plate as anything over the back face would get in the way of the belt. Not sure if this will be enough?
Attachment 17469Attachment 17468Attachment 17470
For the carriages, should it be 'ZA' pre-load? Also how do you define the longer carriages in the part reference and what is the length of these so I can double check the models please?

[Boyan Silyavski]

Yes, ZA preload. BST Automation aliexpress, Fred if you have not figured the provider. You could use my name as reference and he will give you the right prices. Most of the people here buy the stuff from him. Alsmost always he has the best price and most importantly packs very well and stands behind if there is an error or fault

Hard stops also could be 4 big bolts or small plates welded at the sides that the plate that attaches to the ball screw hits them at end of travel. Your looks ok, just dont like the plates at the back of table, better as in front- box section.

The main mission of the hard stops /according to me/ apart of stopping the machine travel, is to stop it at that moment say just 2cm before ballnut travel ends. They must be nearly as possible square as i mount there the limit switches and they are my reference of squareness. So i use straight edge and make them truly square and weld them at the end when gantry is mounted and squared. If you understand what i mean

So i see the real beauty when the machine frame length or say distance between hard stops at the end of frame is = (desired travel) + 2cm
where travel = ball screw length - length of the gantry legs) + 2cm

So i know i have not wasted spinning mass that does nothing

[examorph]

Boyan - Thanks for the advise, I will look into the distance and confirm the 2cm as per your comments.

Are there any advantages to using the longer type carriages? Models are based on the shorter ones 'CA', and using the longer 'HA' type carriages will further reduce the cutting area.

[Boyan Silyavski]

Boyan - Thanks for the advise, I will look into the distance and confirm the 2cm as per your comments.

Are there any advantages to using the longer type carriages? Models are based on the shorter ones 'CA', and using the longer 'HA' type carriages will further reduce the cutting area.

Depends on what you want to cut. as they are very similarly priced and i wanted to cut aluminum i like the long ones. But i like also to overbuild a bit :-) . For wood i dont think it matters anyway

[examorph]

I also want to be cutting aluminium, so updated the models with the longer carriages (CAD models from here) and replaced the rear hard stops with large bolts (will use a steel plate spacer on the inside of the box section to support these). One thing I cant figure out is if I was unlucky enough to hit the hard stops, would it not end up distorting the frame and cause more problems?

Anyways, the larger carriages didn't make that big of a difference to the work area and seemed to fit OK with the existing setup (slight overhang though) so all in all, seems to have worked out ok.
Attachment 17484Attachment 17485Attachment 17486Attachment 17487Attachment 17488
I have shown carriage spacing for each axis. Can I reduce or need to increase it anywhere?

[examorph]

Do you guys thinks i'm now OK ordering in the linear components? If so, hoping you could help me with a few things:

Linear Rail -
2 x Hiwin HGR20- 300mm linear rail
2 x Hiwin HGR20- 600mm linear rail
2 x Hiwin HGR20- 1050mm linear rail
12 x HGH20HA ZA Hiwin block
Do you normally tend to specify the accuracy and dust protection indexes as part of the carriage/rail refereces when ordering from Fred Lee?

Ballscrew -
1 x SFU / RM 1605-L250mm Overall length- C7 ballscrew with a ballnut with end machined and increase dimension F on end machining to 30mm for pulley
1 x SFU / RM 1610-L650mm Overall length- C7 ballscrew with a ballnut with end machined and increase dimension F on end machining to 30mm for pulley
2 x SFU / RM 1610-L1050mm Overall length- C7 ballscrew with a ballnut with end machined and increase dimension F on end machining to 30mm for pulley
4 x BK / BF 12 support for ballscrew

If you spot anything out, please let me know.