Black pipe questions

[ljoe1969]

I am considering drawing some plans for a homemade Cnc wood router. The cutting area is 18" x 24".

My question is would 1" diameter pipe be sufficient for this span?

Would it need to be braced to keep it from bowing in the middle?

etc....

[HuFlungDung]

1" black pipe is pretty crappy stuff to use for your rails. Its not smooth, and there isn't anything about it that is 1"

[CNCadmin]

I'd go 1.5 or better, you don't want any flex.

[anoel]

I'll second Hu and CNCAdmin's comments. Having used "Black Pipe" myself. Drill Rod is affordable and has excellent tolerance. I'd recommend using it instead. Your 1" drill rod will flex much less than the 1" pipe will. still if you can swing a bigger Diameter you'll be better off in the long run, unless you enjoy building a second machine to overcome the weaknesses of the first.

[xairflyer]

This guy has used pipes for his with a fairly large span.
He has added a support in the middle.

I came across an electrical Conduit pipe which is made from stainless steel and has a ground finish, - nice stuff.

http://home.comcast.net/~machinecnc/...nc_router.html

[Mr.Chips]

Black pipe is widely used on Crankey's machines and many of the ones seen on this Forum.
The size and weight does definately have an effect on the black pipe. And if you are building one larger than Crankey's designs you possible will need larger or different material.
In this Forum Chuckknigh is making a pretty good sized machine using black pipe and he has addressed the problem of pipe flex by installing a piece of wood that has been chamfered at an angle so as to contact the pipe and minimize the flexing of the pipe.
Here is a photo I borrowed from his photo showing his approach the the flexing problem.
Hager

[HiString]

This raises a question or two for me....................(OK, I'm a total newbie and still in design stage), but enquiring minds need to know

I'm planning on having a total X-axis length of between 30" - 36" and will be using solid steel (not stainless) for the rails. Motors weigh approx 2 lb each, gantry will be aluminium and initially I will be using a Dremel...........the main use for the machine is to engrave lettering in aluminium plate (front panels for audio equipment).

Armed with this knowledge, would anyone care to give some advice on rail diameter or any other factors I need to consider.

[ger21]

I'm using 2" EMT tubing. It's only $10 for 10 ft. A 3 foot section is pretty stiff. Mine is not suspended, though. The 2 pieces are held in compression to a wooden framework. Here is a link:
http://www.cnczone.com/showthread.php?threadid=1356

Like I said, if you only need a 3' span, It's pretty rigid.

Gerry

[ljoe1969]

has anyone considered using angle iron for the rails?

[balsaman]

Keep in mind, that many home made machines are built to cut stuff like model airplanes and toys out. Black pipe works great for this type of machine. The loads are light and the accuracy will be such that you need a vernier to see that it's the wrong size...Its all about what you will use the machine for.

If you wan't to cut metal, buy a milling machine and convert it. If your cutting balsa or plywood, use what works and what you can afford.

Eric

[HuFlungDung]

I'd look more closely at using any of many C1018 cold drawn round or square steel products before I would waste my efforts with black pipe. For a small machine, the difference in price isn't going to break you. There is little point in sabotaging your own efforts with an inferior foundation (the rails) to begin with. That's just my opinion. When building your own machine, you're saving enough money anyway, that you should be able to sink a bit more into better materials. That is how I look at it when I build something.

[chuckknigh]

Here is a photo I borrowed from his photo showing his approach the the flexing problem.
Hager

I like that little work-up you did, Hager. Thank you! May I borrow the picture? It makes the forces pretty obvious, I think.

OK, explanation time. The gantry will force the rails outwards, but that's not the only force vector present. You also have to address the gantry's weight, i.e. gravity, with a force vector that would be drawn "downwards."

Think back to vectors in high school or college -- add the two of them. You end up with a combined vector pushing outwards diagonally, both outwards and down, at the same time... So, as you can see from the picture, my rails are below, and the chamfer pushes them "in." Simple, but not necessarily obvious.

-- Chuck Knight