CNC Router New Build

[Ross77]

Martin has pretty much said it all.

Profile rails are much better but are are less tolerant to mounting errors so if you have limited access to tools then you will need to shim and grout to make them level. Otherwise you will lose the advantage of them.

Supported rails can absorb some mounting error but at the cost of rigidity as they have a larger radial clearance. TBR blocks have adjustable clearance so you can maximise their rigidity (data sheets show lower load capacity but I think that is because they are rated with max clearance, need to check that tho.)

For plastic and ali I would go for the 5mm pitch screw to keep the torque advantage. You can always gear up if using belts. Diameter is dependant on length/speed but 16mm should be ok.

There are so many options its probably best to Post some designs to help further. Good luck

[martin54]

For plastic and ali I would go for the 5mm pitch screw to keep the torque advantage. You can always gear up if using belts. Diameter is dependant on length/speed but 16mm should be ok.

Ross obviously I got this one wrong, still learning myself & haven't started machining yet other than a few test pieces. Reason I had said 10mm pitch screws was because I was under the impression that you had to use fast speed & feed rates for cutting plastics. Have I got that wrong or would you just gear up 2:1 for that.

[Ross77]

For plastic and ali I would go for the 5mm pitch screw to keep the torque advantage. You can always gear up if using belts. Diameter is dependant on length/speed but 16mm should be ok.

Ross obviously I got this one wrong, still learning myself & haven't started machining yet other than a few test pieces. Reason I had said 10mm pitch screws was because I was under the impression that you had to use fast speed & feed rates for cutting plastics. Have I got that wrong or would you just gear up 2:1 for that.

No not wrong at all. I just think that for Ali and plastic 5mm would be safer as the Cutting force is higher with Ali than plastic. If the speed is an issue then yes it is a simple job to gear up as plastic is lower cutting force and the steppers are 3.5N

You could take the other approach of gearing down a 10mm pitch which gives the same speed/force but the 10mm ballscrews are less rigid than the 5mm so you would lose out there.

Theres no real right or wrong way but I figure it is best to make it as mechanically as strong as poss and then pick/upgrade motors later.

[PilotTom]

Thanks for the advice Martin and Ross.

I have made a start on some designs after reading through a heap of build logs. Seems that for my size of machine I would be pushing the budget too far to get HIWIN 15mm rails on all the axis. Perhaps I will have to have HIWIN on the Z and build in some upgrade paths for HIWIN on X and Y in the future if I find the machine needs it.

Also thanks for the info on welding problems in regards of accuracy. I think I should be aiming for something similar to this one, in particular JAZZCNC's machines in the second post of this thread http://www.mycncuk.com/forums/diy-cn...ign-build.html

The info on the screws is useful too. I hadn't anticipated the torque required for aluminium, I was worried about whipping. Speed is of secondary concern after the accuracy. I would rather run for 10hrs and be accurate than 5hrs and be sloppy. I will design with pulleys so I can have a bit of choice over it.

I am having trouble finding Aluminium profile with prices listed to get a feel for what is affordable. Are there any preferred suppliers? I need to get a feel for how much I can expect to spend to help with design choices.

Thanks.
Tom.

[martin54]

Try doing a search Tom, suppliers have been mentioned but can't really remember who as it's not something I have bought myself. I do remember JKN Ltd & value frame being mentioned but can't say for what reasons. May help with the search though. Aluminium warehouse are pretty good if you need full lengths of flat bar or tube but don't think they do profile.

[MikeyC38]

Thanks for the advice Martin and Ross.

I have made a start on some designs after reading through a heap of build logs. Seems that for my size of machine I would be pushing the budget too far to get HIWIN 15mm rails on all the axis. Perhaps I will have to have HIWIN on the Z and build in some upgrade paths for HIWIN on X and Y in the future if I find the machine needs it.

Also thanks for the info on welding problems in regards of accuracy. I think I should be aiming for something similar to this one, in particular JAZZCNC's machines in the second post of this thread http://www.mycncuk.com/forums/diy-cn...ign-build.html

The info on the screws is useful too. I hadn't anticipated the torque required for aluminium, I was worried about whipping. Speed is of secondary concern after the accuracy. I would rather run for 10hrs and be accurate than 5hrs and be sloppy. I will design with pulleys so I can have a bit of choice over it.

I am having trouble finding Aluminium profile with prices listed to get a feel for what is affordable. Are there any preferred suppliers? I need to get a feel for how much I can expect to spend to help with design choices.

Thanks.
Tom.

Hi Pilot Tom
Hope you are getting on well with your design. I have worked up the final drawings and going with Jazz's approach on the use of 80x40 heavy extrusions arranged in an L pattern, with 20mm toolpate for the Z axis and 20mm plate for the gantry sides. After just purchasing a VFD and 2.2kw spindle, it sure is heavy! so stiffness of the gantry is important.

The guys on this forum give honest critical advice which has made the difference in my design and will ultimately save time and money. My buiild will start in a couple of months so watch the build log.

Kind Regards
Mike

[Ross77]

I have worked up the final drawings and going with Jazz's approach on the use of 80x40 heavy extrusions

Ditto on using heavy sections, I bought a job lot cheap on ebay a year or two ago and it was a mix of light and heavy, the light is much weaker and only really any good for display cabs.

Perhaps I will have to have HIWIN on the Z and build in some upgrade paths for HIWIN on X and Y in the future if I find the machine needs it.

If you can, go for the profile rails on the z axis as this is always going to be the weakest section, loaded as a cantilever and also eccentric loading from the weight of the z axis.

20mm plate for the gantry sides.

Ok this is only my opinion and I realise that there are lots of machines thathave been built this way and work fine but to me it is a very inefficient way too do it. The gantry sides are the final link in the chain of transmitting force to the ground so really need to be treated as beams/columns. I would go for using 4040 extrusion with 6mm plates either side, probably the same weight but much stiffer. Again I'm not criticising using plate, it just not the way I would do it.

[davethefixer]

Having nearly finished a build similar to what your describing (mine having a cutting area of 1200X700X200)
Welded box section steel frame (50x50x3)
45x45 heavy aluminum profile frame (on top of box section)
20mm profile rails on all axis
2x1500 2010 ballscrews for x axis, 1x1000mm 2010 ballscrew for y axis, 1x250mm 1605 ballscrew for z axis
20mm side plates (milled with my home made MDF router) (very very slowly)
electrics, stepper drivers x3, (from diy MDF special)
2x nema 34 (for x and y axis) 1x nema 23(from mdf special)
belts and pullys ect. ect ..... a bit over engineered?? oh yes !!! cost...................way more than i had expected (around £2.5k) 5 months to build....
suppliers i got materials from
http://http://aluminium-profile.co.u...KJN990520.html
http://http://www.zappautomation.co.uk/en/
http://http://www.aluminiumwarehouse...php?cart_qty=2
http://http://www.beltingonline.com/...leys-bars-272/
http://http://stores.ebay.co.uk/line...earings?_rdc=1
and a big thanks to iwant1 as his build log was exactly the sort of thing i wanted to build
http://http://www.mycncuk.com/forums...my-head-7.html
hope this helps