Re: questions before building

--- In CAD_CAM_EDM_DRO@y..., "andrew_k_jones2000" <andrew_k_jones2000@y...> wrote:

> Hello List,
>
> I have a couple of general questions that I could not find answers to
> in the FAQ. I have searched in the archives a bit, but the amount of
> posts is making my particular questions hard to find since they
> contain some very common keywords. If anyone can suggest threads
> where some or all of the questions are dealt with, I would be very
> appreciative. I could read these threads and come back with more
> refined questions.
>
> Over the last year I have been collecting surplus hardware to build a
> CNC router. I now have 4 Nema 23 steppers with optical encoders, 4
> CMD260 micro stepping drives, a parallel port interface board (EMC
> compatible), and other bits and bobs of thrust bearings, drive
> couplers, etc.
>
> The material intended for milling and routing is Perspex, plastics,
> aluminium sheeting, wood, and general soft metals (just hobby
> stuff). I am thinking about driving the axis with threaded rod, and
> using brass bushings on solid rod as the axis guides (e.g. like many
> have already done). The design will be a gantry style, with 90cm x-
> axis, 70 cm y-axis, and 10 cm z-axis.
>
> Initially I was going to use a hobby rotary tool for the spindle
> motor, but have decided to first look at something more powerful to
> base the z-axis design around. I figure it would be easier to alter
> a set-up made for a cutout tool to accept a small hobby rotary tool
> than visa versa. I also thought that if I am making this thing, I
> might as well not limit myself from the start. I can always go
> backward to the rotary tool I already own.
>
> My questions are these.
>
> Motor suggestion/recommendations, things I should consider:
>
> I am interested in finding a motor that is... in order of importance:
> able to cut the above materials, quiet-ish, light; accept variety of
> tools (cutting, routing, drills). I am not expecting to find the
> optimum for all these categories in one tool, but some balance. With
> thread-rod, I don't expect the feed rate to be blistering, but I
> would like to not worry about going slower to accommodate the motor,
> and I may upgrade the drive system at some point.
>
> Adaptability of the motor in holding tools:
>
> I am also wondering about the tool holding ability of these motors
> (cut out / router). Can one use a variety of tool shaft sizes, or
> are they limited to a standard diameter, and thus maybe rule out
> small drill bits and accessories (pcb drilling, etching)? I am
> planning to have the ability to attach my rotary tool for smaller
> jobs, so it crucial. But I might pick one motor over another if it
> has more versatility in what it could hold.
>
> X-axis coupling
>
> I am planning to have two x-axis drives. Is coupling these
> electronically (splitting the x-axis step and direction to two motor
> drivers) a good route to go? Should I mechanically link the axis
> drives with a belt? And if so, should I leave the second stepper
> inline? I do have optical encoders on the steppers, and though it
> might be possible to have each x-axis stepper act independently, but
> always carry out the same command. I could then use the feedback of
> the encoders to make sure that x-axis and the "4th-axis" steps were
> successful. I am definitely attracted to the just coupling
> electronically, and counting on relatively few miss steps... not sure
> if this is reasonable.
>
> Thank for any help or advice you can give
>
> Andy

In your circumstances i would consider a small variable speed plunge router. I suggest the type of router design where the motor can be removed from the baseplate and plunge mechanism could be valuable as you could change to different motor\cutter assemblies easy. You may be able to use the plunge mechanism for z axie if you can reduce any slop in it.

Routing thermoplastics must be done at lower speeds or you get a gooey mess, sorry got no idea of ideal bit speed but I do rout plastic on an ordinary bench drill without this problem. probably 2-3000rpm

I have seen reducing sleeves that enable small shafts to fit into 1/4 inch routers, if I can get them in australia you must be able to get them in usa.