5 1/4" Cnc

[Rance]

Well, the time has come, the Walrus said for me to start a build log for my first machine. I havn't cut any wood yet but I've been planning and designing for a few weeks (ok, months) now so don't consider today as the start time. I don't know how organized this will be but I certainly will have a WIDE VARIETY of questions I'll be asking here. Or should I post those questions in the general area with specific topics and keep the focus of this thread on just the build? That might help others 'search' for answers easier.

The OFFICIAL name of my machine....... CNC525

PROGRESS:
I'm gonna try something a little different than most others here. This #1 post will serve as a 'Living Table of Contents' for others to use to navigate my build. I'll try to update this post as appropriate.

MACHINE PURPOSE:
This initial machine will serve as a training ground for me to learn CNC but should also be useful for small wood routing and some PCB Isolation Routing/engraving.

GOALS:
I expect to build it at a minimal cost and all that goes with that (< $150 for everything, and I mean everything). I expect to use as many scavanged materials as possible to reach that goal. I'm expecting a precision of +-0.005" (understanding that this may limit my PCB routing abilities). The expected working area will be about X-16" Y-8" Z-3". Special building tools required will be limited to a Table Saw, and a Drill Press. Construction materials will be mostly Plywood. Rails will be Angle Iron with Inline Hockey/Skate Bearings. Lead Screws will be cheap threaded rod (1/2-10). For motors, I'm hoping to use stepper motors from 5 1/4" Teac floppy drives, hence the name of my machine "5 1/4" CNC ". If successful, I'll also be able to use the controllers from those same Floppy drives. Otherwise, I'll move up to Steppers from HP Laser printers with home-built electronics (PicStep, or similar). I guess I'll have to change the name too. If the Floppy Drives work out, I plan on using PC Power Supplies for power. And lastly, the spindle will be my existing Dremel tool.

Gantry Design:
Initial pics

[Rance]

CAD Design Software:
I'm initially committed to learning & using Alibre Express for my CAD work. I'll be using it for both the design & layout of this machine as well as for the design of 2D & 2.5D parts I'll be cutting on my machine. If anyone has any comments on why I shouldn't proceed with using Alibre then please speak up NOW. BEFORE I get too used to Alibre's interface. I'm just looking to avoid as many pot-holes as possible.

I'd like to initially be able to stand on the shoulders of those who have gone before me and take someone's Skate bearing drawing and just modify it for my own purpose. Anyone got one that they can post that is loadable into Alibre Express? Thanks in advance for any & all submissions. If it helps, its 'like' the one in the right side of this post http://www.cnczone.com/forums/showpo...81&postcount=8 .

That leads me to... What drawing format is most exchangable between folks here, DXF, DWG, others? Thanks.

[Rance]

Well, I'm still getting my head around Alibre-Xpress. Making lots of progress in my drawing abilities within the pkg. I've modeled the bearing assembly on the side of the gantry. Note the difference from others where there is NO guide board above the bearing assembly. I have incorporated the use of some 'Pin' bolts and associated 'Cup' bolts (that accept the pin bolts) to stabalize the bearing assembly in the X and Z axis to the gantry side.

I'm not entirely pleased with the 3 pics here so I'll try to also post my Alibre files if someone can use them to get an idea of what I'm doing. I'll try to get better at the pic thing as I go along. Enjoy.

[Rance]

PS: Due to the limitations of my 'Free' copy of Alibre, I've used my 'Pin' bolt for all bolts. The ones that bolt the bearings to the angle iron will be just long enough. Also note that the triangle piece of wood between the angle iron and the bearing block will need to be fashioned to not interfere with the bearing bolts or the T-Nuts, etc. sticking out of the bearing block.

The nice thing I can figure out with this though is whether or not (with my dimensions) my top and bottom bearings will have enought clearance between each other. So far so good.

[Rance]

One item to note is that the countersink in the 'Cup' bolt is 82 degrees (standard for a counter sink) and the point on the end of the 'Pin' bolts is 90 degrees. This should make the tip of the bolt ride on the lip of the 'Cup' bolt rather on the bottom giving it better stability. Also, the dimensions will be such that the 'Cup' bolts will be as near as possible to the T-nut on the gantry sides, again for maximum stability. I've included a pic so you can get a better idea what my 'Cup' bolts look like.

[spalm]

Hey, Rance, looking good.

Do you have a link for those pin bolts? I take it that the pin bolts are blue (with the female, or cup as yellow) and regular bolts are green and the grey things are Tnuts? You sure you don’t want to add the upper and lower wooden guides as added support? I don’t think this is a place to worry about overbuilding.

Steve

[Rance]

Steve,

Its in the zip file... {loooong pause} Dooooh! OK, I think I understand now what your question really was. The pin bolts are simply standard bolts that will be chucked in a drill and the ends sanded/filed to a 45 point. The cup bolts are also homemade, first drilled with prolly a 1/8" hole then use a countersink. Does that help? I actually have a procedure documented for that process. I'll post that later.

As to having the wooden brace, I see that as a weak point to the current designs. I see the resistance to horizontal motion and flexing of the gantry partly coming from the bolts having a long moment arm to securing the bearing assembly to the gantry side. If the guide boards (that I am leaving off) are to help at all, then the fit of the bearing assembly between them would have to be overly tight. I can't imagine the current machines 'actually' being built that tight.

Of course this is one of the reasons I consider this machine my proof-of-concept machine. It gives me the new experience of working with skate bearings against the angle, this modification of the bearing supports, and with getting a hands-on feel of the rigidity of a torsion box. We'll see if it actually pays off or if it is a flop. I'm going on pure assumptions and gut-feel with these design changes.

PS: And your color assumptions are correct.