Re: suggestions for largish gantry for laser (and possibly router)

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "skykotech" <rick@s...> wrote:

>
> Sigh. First I had a sherline cnc with, IIRC, about 4" x 10" travel.
>
> My wife was always coming up with things she wanted made that

needed

> just a few more inches travel.
>
> Then I got my shizuoka with 29" x 15.5" x 16" travel. Last night

we

> were cutting tombstones out of 1" foam with my 17 watt CO2 laser

and

> kept running up against the travel limits again! lol. I ended up
> taking off the rear way cover to get an extra 2" of y

travel...sheez.

>
> So now my wife is pushing me to build a 4' x 8' cnc router/laser
> engraver so we can just toss in full sheets of plywood, mdf, foam,
> etc. Since it is not all the time that your spouse wants you to
> spend lots of money on machinery, I figure strike while the iron is
> hot. :-)
>
> I am thinking about building something out of welded square tubular
> steel stock. Someone either on here or the emc group built a chain
> drive router with angle iron ways that was actually relatively
> accurate when milling even aluminum. That sounds like a potential
> route for me to take. Pitty my welding skills are so poor...
>
> The forces for the laser are negligable. I have a 50 watt laser I

am

> thinking of mounting to the gantry frame parallel to the 8 foot

axis

> that fires into mirrors moving on the y axis. Pretty standard way

of

> doing this..shouldn't be hard.
>
> I also want a machine that can route through a full sheet of 3/4"
> plywood. The laser is not strong enough to do that, so I need to
> build this machine rigid enough to support a wood router.
>
> How many people have had success with the angle iron/chain drive
> setup?
>
> thanks,
>
> Rick

Whew, you had things pretty easy to design until you threw in
the "cut through a full sheet of 3/4" plywood" clause. Do you mean
in one pass? If so, that's gonna take a lot of router and a lot of
motor torque to shove it through without burning. If you can live
with multiple passes then I can stop hyperventilating!

I will give you a few words from the trenches: Building mixed
machines ends up with compromises. What I am saying, is that the
torque/speed ratios for a router are far different than for a laser,
plasma or low force cutting. Normal home owner type routers need
slower cutting speeds with plenty of rigidity in the structure and
high to moderate cut forces at the tool. That would normally
indicate a drive mechanism that is geared down or has a smaller
ratio. The other consideration is the dust collection and protection
of moving parts. Once again a router puts out a lot of dust and
dealing with that is part of the design. A laser needs little in the
way of dust extraction as does an engraver.

The cutting speeds on a laser cutting foam, probably need to be a lot
faster than a router that will cut at 30 to 60 IPM depending on the
bit diameter and the material.

I learned my lesson from building a combo plasma cutter and router
table. I designed a nifty slide-in cutting surface that can be
changed out between a grid or an aluminum frame and MDF surface. The
water tanks will slide in and out in a lower set of slides. I built
the gantry stout enough the handle the router and made a universal
mounting plate on the Z axis to mount any kind of tool I wanted.
After using it first as a router then switching over to the plasma
cutter it has never been used as a router again. The upper end speed
is just a little too slow for plasma (180 IPM) when cutting thin
stuff but the gantry will knock down Superman.

The substructure is all welded square tube. The gantry is all 1" X
3" extruded aluminum (some 3 X 3 pieces). I used some used 8020
pieces for a lot of the gantry build.

I can see combining a laser and maybe a small rotary cutting tool or
even the engraver (plan on designing a floating Z head for the
engraver) but you will have to either grossly overbuild the drive
mechanism to add a large wood router. Since you will need both speed
AND torque you will have to design to both needs. I also think a
design based on servo's is more flexiable (that's what I ended up
using or things would have been a lot worse).

As for the chain drive: It will work and is rugged but once again,
for non-contact cutting way overkill. The guy you are talking about
with the angle iron and chain drive is Russ (don't remember his list
name). He tends to fad in and out from the list from time to time.
You might post a ping over on the MACH1MACH2CNC list where a lot of
us hang out. He uses that controller software so may monitor that
list more tightly.

If you do the combo it will be like building an airplane/boat/car
combo. It may look a little funny and not do any of the things as
good as a dedicated machine but it will work.

I have a separate engraving machine (my first creation made to
engrave stainless steel mechanical pencils). I sits gathering dust
at this time. I plan on starting a dedicated plasma cutter with all
of the things I have learned and turning my combo table back into a
dedicated router.

I don't say these things to discourage you. On the contrary. If my
wife told me to go build bigger and faster machines I would first
check to make sure I was awake and not overdosed on any substance,
then rush out to the shop and start sorting through my "stash" of
surplus (right after I called Gecko and ordered some more 340's!)

You obviously have some experience in building some machines but you
have to think about different drive mechanisms for big tables.