[chithinh]

Hello all,

I just finished design a CNC machine. I would like someone review my drawings and give me your idea about this one. If is it able to working?

Thanks .... Chi Thinh.

(note: If you want to receive all drawings please contact me via email at address is [email protected])

[dertsap]

looks good ,when do you start

[chithinh]

I have made some parts. I am looking forward to receiving driver board from US. I order this board from hobbycnc.com. Now i don't have many free time to do this one. I only do it on every weekend.

[Greolt]

Your design looks pretty good Chi.

The only thing I would say is maybe make the bottom of the gantry where the bearings are for the X axis a bit wider.

Or separate the bearings a little more. You will lose a bit of X axis travel but you can reclaim that by making the table that much longer.

See the pic below. Look forward to seeing the pics when you make a start.:cheers:

EDIT: Second pic, you could also look at leaning the gantry back a bit.

As you have drawn it the spindle will be off the table when the gantry travels all the way to the other end.

These pics are very rough, just done in Paint to show what I mean.

Third pic is your drawing.

[ZipSnipe]

I agree with Greolt, and I like his second idea of having the gantry lean back, this would give ya a little more travel in the x axis.

[dertsap]

better balance as well

[la_coterie]

I agree with Greolt, and I like his second idea of having the gantry lean back, this would give ya a little more travel in the x axis.

Hows that work then? for the same length X rail it will still move the same distance, the only differences are, a) cut area starts further back and b) the shape is harder to cut out!

Yeah, make the X axis bearings wider apart. What travel Y have you got? with a single drive in the middle I reckon it will slew when cutting at one side, a ball screw each side will be much better.

[anoel]

Looks like you are planing to use unsupported rails... = A sagging log axis. And a not so sturdy short axis... Spend the extra $$$ and use supported rails and you'll end up with a nice machine.

[jsage]

The leaning back brings up an interesting question implied by some your comments. Does that configuration work best for static or dynamic loads. Oversimplifying I'd expect the router creates upward force on the front of the gantry downward on the back side. Same goes for lateral. One of the recent designs I've seen speaks to centering the router. Downside for me you have less flexibility in what can be mounted to it. Footprint of the gantry and tool connection seem more straighforward.

[Coogrrr]

So I read this thread and I figured my .0002 is as good as any so here goes.

It is irrelevant as to the design you choose. The relevance is in the products quality of parts. I attach a drawing of both the lean back and straight verticle examples (crappy i admit). Please note the little red circles...

Theses circles are some examples of where load stress can occure and then result in a problem. if the verticle machine is made of better materials and built more sound the lean back is irrelevant if the lean back is made as well then yes it would afford some tighter tolerances but at some point you run into the uncontrollable items like the quality of the router itself the deflection of the bit used the product being milleds deflection etc etc.

Now I say all that to mean this wether you use double gantry or lean back or a regular jgro build the deflection is ZERO at no movement or should nearly be if the bit is straight. The deflection is crippling when you feed 12349ipm (ok little far fetched) but the better built the machine regardless of design means more IPM with less deflection is all and likely a well built lean back or straight down or double gantry machine will give you great tolerances.

If you need more then .001 or .005 lets say then think of building a very solid machine that moves slower like the guys over in the jewelry section they build what I think are engraving machines that will shame any attempt I may make. I however am not trying to engrave fine jewelry and art onto the head of a pin. I take my hat off to those guys WOW. I will be doind some custom wood stuff that will get fairly tight like maybe 0.001 and I would be very happy if I can make that with my machine but wont cry if it only gets me to within 0.01 as a hundreth is real nice!

I think the designs on this thread are awesome and I am interested in the leanback design just for the sake of X travel.

just my .0002 worth

[la_coterie]

...and I am interested in the leanback design just for the sake of X travel.

Again I ask how does this increase the X travel?

Good points on the stress areas, the only advantage of doing a leanback, if designed properly, is that the cutting tool is between the X axis bearings (looking from the side) so evening out the stresses & strains better

[jsage]

Good info. Need a little more time absorb. Still trying to figure which is x and which is y. I'm down with z ; )

[Greolt]

Again I ask how does this increase the X travel?

Take another look at my thread above. #4 The third picture is Chithinh's original design.

Now visualise moving the gantry to the other end of it's travel.

The spindle is now off the table. That would not normaly be considered within the cutting envelope.

Leaning back the gantry in this case increases the usable X travel. As well as other benefits.

[la_coterie]

Hi Geolt,

I see what you mean on this design. Although as has been discussed the bearings on the X rails appear too close together. your post No 4 piccy 1 seems the simplest answer.
One could just offset the table forward in relation to the rails. (if you have the room)