[prodigy86]

Hi,
I'm in the middle of designing a cnc router out of 40 x 40 bosch extrusion as i can source it easily, ive put 80 x 40 round the top to strengthen it, the side and gantry will be 10mm aluminium

ive made it to use linear guides but may change to rails yet, undecided.

its my first build so still very new to this, reading as much as can in time i have, so was hoping if someone could let me know if im on the right tracks and if my frame looks ok and solid enough or if changes could be made before i go much further as ive just learnt this cad program and its pretty time consuming at the min, getting abit quicker more i do tho

im planning on using a hitachi mv12, which i would like to cut wood/plastic and aluminium






any advice, is very much appreciated

thanks


e2a: attachment

[PaulRowntree]

Hi!
I would stiffen the gantry sides with some edge-on elements (eg the same thickness (or thicker) projecting 5-8 cm away from the vertical pieces, running the full height of the gantry sides). Plus, if you could bring the under-the-table cross piece up closer to the table underside it would make it stiffer.

I don't know the X-Y dimensions of your table, but the open areas seem large to me, and the table top may deflect down under cutting forces. Can you add more cross braces?

[prodigy86]

the dimensions of the frame are 1000 x 750mm, it could be made smaller if necessary.
yeah would be no probs putting in extra extra cross braces, ive attached a pic of the under cross piece and would be able to come abit yeah.

but sorry if seems a daft question but how you mean by stiffen the gantry side with some edge-on-element?

thanks for your advice

CNC ROUTER5.pdf

[PaulRowntree]

t

but sorry if seems a daft question but how you mean by stiffen the gantry side with some edge-on-element?

CNC ROUTER5.pdf

Not daft at all ... I explained it poorly. The absolutely easiest way to make a beam stiffer is to make it thicker. A 10 cm thick piece bends less than a 1 cm thick piece. But this is expensive and heavy. The next best is to make a shape like a hollow tube. For example, a steel rectangular tube, 5cmx5cm
with a 5 mm thick wall is about 75% (by memory) as strong as a solid 5x5 piece. Most of the stiffness comes from the edges middle, not the middle. What you ar e really doing is moving as much of the material as far as possible from the centre line of the beam. Maximum stiffness for minimum weight (and $).

Another approach is to add stiffeners that are attached at right angles to the existing plane of the Al gantry pieces, running top to bottom. You could have a 3 cm x 3cm bar bolted on, but as you make this thicker (extending farther from the gantry side) the stiffness goes up very rapidly. For a given mass of stiffener, it is much more effective to make these stiffeners extend farther from the gantry than thick.

For example, imagine a board lying flat. You can make it stiffer by adding another piece to double the thickness, or you could attach the second piece at right angles making a 'T' shape. This second way will resist bending MUCH more than just doubling the thickness. It doesn't take much extra material to increase the stiffness by 2x to 3x.

You can play with these bending ideas by downloading the free program Beam Boy and see how different shapes affect the stiffness.

Does this make more sense? Too many words, I know ...

There is a great thread here from ~a year ago with good photos. I will try to track it down ...

[kevincnc]

That's a good start, and good advice from Paul. It doesn't look to me like the rectangular bottom section will add much to the strength or rigidity- you might be better off eliminating the long extrusions there and using the short ones on the top section for better table support. Like Paul said, bring the cross-piece under the table higher up if you can, and make the legs at the corners as short as possible.

[prodigy86]

ah yeah a get ya PaulR, ill have a look and think whats best to use and to go about it and put it to my drawing, mabye i could use the 40x40 extrusion to strengthen the side?
ill have a look through some other builds get a better idea also, thanks for advice

ill mess about with the rest of the frame, see what can do to get it more sturdy

ill be back with the update

thanks

[PaulRowntree]

Unless you have lots of extrusion looking for purpose in life, I would just go with a square steel tube, bolted on the outside of the gantry side at 4 or 5 places. I think a 2"x2" x0.25" wall piece of steel would be stiffer than Al, but you would have to compare the moment of the two cross sections. Steel has a 3x strength advantage over Al for the same value of I (ie pieces of the same shape and size).

Cheers!

[dmalicky]

Yes, a good start and good advice above. Some thoughts...
- I can't tell the dimensions, but maybe make the pair of bearings sharing a rail a bit further apart. That lowers the load in each, improves stiffness, and minimizes racking.
- Raise the main rail/bearings to be the same height as the table top. Then cutting forces have a smaller lever arm to torque the gantry, smaller loads on the bearings, more stiffness.
- Most important for cutting aluminum, make the main gantry cross member a square or rectangular tube with at least 4 bulkheads evenly spaced along its length. For least weight and greatest stiffness, use a large width x height and a thin wall thickness. For your travel and z height, I'd suggest an aluminum square tube around 150 x 150 x 4mm.
- Also for cutting aluminum, make the distance from the table to the bottom of the gantry as small as your needs require.

[louieatienza]

Yes, a good start and good advice above. Some thoughts...
- Raise the main rail/bearings to be the same height as the table top. Then cutting forces have a smaller lever arm to torque the gantry, smaller loads on the bearings, more stiffness.

While I agree with your other thoughts, from what I've researxhed and understand is having the leadscrew on plane as close as possible with the bearing blocks?

[OCNC]

Ideally you want the drive line and bearing line for each axis to be as close as possible to each other and then the combination of drive line and bearing line for each coplanar axis to be as close as possible to each other in the coplanar sense and also as close as possible in the coplanar sense to the line of the cutting force. The mechanicals of the 'ideal machine' would then be very 'thin' in the Z direction.

Chris

[Drools]

your machine design is very similar to mine in size and materials, except I used 3030 (3"x3") extrusion for the frame sides, 1530(1.5"x3") for the ribs and 6030(6"x3") for the Y-axis. My gantry uprights were made from 3/4" Ali.
I made some legs from laminated Baltic Birch which have worked great so far.
http://www.cnczone.com/forums/cnc_wo...thk_cncrp.html

[dmalicky]

While I agree with your other thoughts, from what I've researxhed and understand is having the leadscrew on plane as close as possible with the bearing blocks?

Thanks, good catch. I've been in dual drive land too long.
So for single leadscrew, as high a plane as possible for both.

[prodigy86]

Unless you have lots of extrusion looking for purpose in life.

Cheers!

that is exactly what i have, haha

im going to have a look about and ask my work what the can get hold of, and update my design to make things stronger and follow the advice given as i want things doing right first time or as good as, rather than wasting time and money.

appreciate the advice and ill be back with it updated to see if things look abit better

thanks for the replys

[prodigy86]

hi,
been very busy lately so the router went on the back burner for abit but hoping to get back on top of things now

ive updated my frame, ive copied drools approach and going to add the legs similar to his. the's a few things i think i will need to change like lower the gantry abit but will see when ive got the z axis and router on first to see how much room i have and im going to put brackets on all corners of the extrusion.

but would like to see if im on the right track before i go much further as i need to use my time wisely.

also i havent ignored the advice about using box section its just i had the extrusion already modeled up and i have more than i know what to do with so it would be easier for me to use but if you think box section would still be better for me to use ill look into getting some

anyway thanks for look and your advice is hugely appreciated

[Drools]

I liked the first design for the gantry better, if the sides were at least 3/4 Ali and instead of just 2 cross members use 4. For the bottom of the gantry use 3 instead of 2.
I didn't angle my gantry risers on purpose, so I could get some over-hang off the end of the table and it was easier to source the narrower Ali.
The table design in the latest draft looks quite a bit better that the first and should work fine, but if you have extra extrusion beef up the table as much as you can.
At this point I would start thinking about how and where you are going to mount the bearing blocks for your screws, and keeping the triangle (Screw, gantry bearings x2) very flat.
Mine works fine with a center driven screw but I did a lot of CAD drawings with the CNCRP bearing blocks to get the triangle flat as I possibly could.
Note: Triangle, when looking at the machine from the end your gantry bearing blocks and the screw driving the gantry will make a triangle. I tried to keep the triangle as close to a flat line as I could.
Also keep in mind this is going to be a heavy machine, make a sturdy base and get wheels rated for twice the weight. I know from experience it is a PITA when your wheels crumble from the weight and you have to replace them.