Thought on Design found on Ebay

[dfranks]

As I am new to CNC I have been doing tons of research before I start building. I came across a German made CNC router table on Ebay and thought it interesting. As I have examined the pics a little closer I began to wonder if the design was good or not. Here are some of the things that I noticed (as a novice of course).
1.) Very thick uprights on the gantry, maybe 1" or better? The width is not much larger than the width of the stepper motors. The height seem to be minimal as well. The overall working area is 15.75"x11.8"x4.3" though a 39.37"x23.6"x4.3" is available and is more of the size that I am looking to build.
2.) There is no bottom to the gantry. It looks like the X axis rails (rods?) may be pressed in? Anyway I was wondering how stable this would be. The horizontal brace(?) connecting both left and right sides of the gantry appear to be thin, almost more decorative than structural.
3.) There are 2 Y axis ballscrews. I don't know why the idea tends to 'freak me out' but for some reason it does. (I realize that you have to use a controller that supports 2 Y steppers.) I am assuming that if you just use 1 ballscrew on the Y axis that binding is going to occur. Also notice the box mounted under the X axis stepper motor. What's up with that?

So any opinions or other observations? I can see where you might save a few bucks on materials with this design. Oh by the way here is the link to this item on Ebay http://cgi.ebay.com/ws/eBayISAPI.dll...522534852&rd=1
You may want to check out their site which is listed within the Ebay ad as it has more pics and a few videos. Hopefully I pasted the pics below correctly.

[ger21]

Thats a pretty light duty machine. Keep in mind that unsupported rails will always have a bit of sag and flex.

3) I like to call that the X-axis, with the Y-axis being the axis on the gantry. I think you're right, without beefing up that gantry quite a bit, it would bind if not using 2 screws. Those little black boxes appear to be the stepper drives.

That's a nice machine for doing engraving or balsa work, but not really designed for anything heavier.

[Dave's_Not_Here]

... looks to me to be tied together with wide Aluminum plate across the back where the logo is placed...

A channel for the the cable runs across the top... does not appear to be intended for any serious structural support...

Looked at their site... they seem to be able to mill Composit, MDF and Billet Aluminum in their videos...

Hummmm....

[Jayson]

I would agree that the x axis being suspended just on the rods is not ideal. This is a similar design to my machine however my x axis rails are supported. I run 2 screws on the x axis of my current machine both briven off the same stepper but when number 2 comes around I will be going to 1. If you are planning to build a machine based aroung this type of design all I can say is modify it a little then go for it...

Hopefully there will be an image of my machine attached to the bottom of this post. Its only a small image but I can take more if required.

Regards,

Jayson Wallis
(Horsham, Victoria, Australia)

http://www.cnczone.com/gallery/showp...00/ppuser/6402

[dfranks]

Jayson - That is very ingenious on how you are driving both X axis ballscrews off of 1 stepper! What is the actual size that you can cut on your table? On your next design did you mean that you are going to only use 1 ballscrew for the X axis or still use 2 ballscrews and 1 motor for each? Any suggestions on what type of drive (controller?) that 2 X axis steppers can be driven by? I'm still researching as to what desigin I am actually going to use. I have been looking at Beezer's design pretty close. It's very close to what I have been envisioning. Now I will have to look your design over as well. Thanks for the comments. Post more pics if you have them.

[spalm]

Maybe the little black boxes are just cheap "project" boxes used to contain the splices of the motor wires to the cables. Not a bad idea if so.

[Jayson]

Hi All,

In the next design I plan on using 1 motor and 1 thread for the x axis, mounted under the table in the centre. The work area of my current machine is 280mm(Y) x 500mm(X) x 100mm(Z). I can not suggest a controller that will allow you to run 2 motors as I have not done anything of that nature. Good luck with your researching and forget ever sleeping especially after the machine is built... Geez I wish I could stay home and play and still get paid :-)

By the way, I uploaded sone more pics to my gallery for you.

Regards,

Jayson.
(Horshan, Victoria, Australia)

[mad.sculpture]

Hi,whilst looking around at different designs i came upon this also.
the bit i thought was good was those 1" blocks you mentioned on y slides supporting x rails because if you as a hobbyist had these cnc'd for you there wouldn't be much to cock up as far as alignment goes,you'd know x&y pretty good,flat sheet(poss thick) accross back between these and also on top and the x would be quite solid for low end machine.
thing is other than the z axis most everything else could come from marchant dice type people and be simple to align.plus if someone started selling 2 blocks like these which could i think be common to each other if you wanted a machine different sizes it'd be so easy to change as determined only by rod lengths really,you couldn't easily screw it up could you?
too much sag in rails, make 20 mm rail all round supported y rails actualy would be easy to do anyway.
wouldn't it be a great alternative to mdf for us newbies.
Never been able to see why marchant dice not do something like this,you can buy all the saddle blocks end end supports but why can't they publish more complete info as to how they all go together,you can by a complete twin round rail axis set but you still have to get the bits machined to take your leadscrew fittings etc and this could introduce errors.the set looks like cool vesatile axis fot 140 quid,but if you look what they charge for that axis with that bit of machining done it's like 500 quid.
as machining in volume brings prices down it makes sense for marchant dice type suppliers to get it done at source and charge a bit for it rather than us lot getting it done piecemeal.
Ross.

[Regnar]

Did anyone notice that the z axis is only supported by the bottom of the rails. Seems it would flex under load.

[marchantdice]

Hi,whilst looking around at different designs i came upon this also.
the bit i thought was good was those 1" blocks you mentioned on y slides supporting x rails because if you as a hobbyist had these cnc'd for you there wouldn't be much to cock up as far as alignment goes,you'd know x&y pretty good,flat sheet(poss thick) accross back between these and also on top and the x would be quite solid for low end machine.
thing is other than the z axis most everything else could come from marchant dice type people and be simple to align.plus if someone started selling 2 blocks like these which could i think be common to each other if you wanted a machine different sizes it'd be so easy to change as determined only by rod lengths really,you couldn't easily screw it up could you?
too much sag in rails, make 20 mm rail all round supported y rails actualy would be easy to do anyway.
wouldn't it be a great alternative to mdf for us newbies.
Never been able to see why marchant dice not do something like this,you can buy all the saddle blocks end end supports but why can't they publish more complete info as to how they all go together,you can by a complete twin round rail axis set but you still have to get the bits machined to take your leadscrew fittings etc and this could introduce errors.the set looks like cool vesatile axis fot 140 quid,but if you look what they charge for that axis with that bit of machining done it's like 500 quid.
as machining in volume brings prices down it makes sense for marchant dice type suppliers to get it done at source and charge a bit for it rather than us lot getting it done piecemeal.
Ross.

Ross, I think you answered your own question...
We offer quality with a warrantee
as for the price
£500 - 30% for our master distributors = £350
3.5 hours labour £157.50 = £192.50 less the price of the stock!
Regards / Kevin

[mad.sculpture]

Hi kevin,
ok, fairy nuff, i'm out of touch with hourly rates having done too many duff jobs lately.I'm used to what the local engineer used to charge my last company i worked for for one offs,but they were to become rolling orders in future so machinist prob. did them as lost leader.

At the time I wrote I couldn't imagine anybody ever using the components without having the holes for leadscrew through the saddle and endframes,specifications may vary but thought there would be a kind of 'common denominator' smallest size that at least could be opened up by customer if necessary.I've got a cheap ass drill press but wouldn't like to go through that size lump of alloy on it.
It's frustrating as a non mechanical engineering person who mainly want's to do cnc art on a low budget in a house i don't own(ie. can't stick workshop in garden)that you need to have a load of machining tools
and the wherewithall/wokshop to use them to be able to make the poduct that will then render many of them obsolete and make it a (relative)doddle to cut accurately.
I was thinking at the time to buy rockiffe plan and try to make it in alloy.
I then saw the rail assembly and thought i'd be able to make just about any machine i'd need for 3 * £140 ish for sliding elements exluding screws
then when i saw cost of machined ready to use item it burst my bubble because I realised it's going to be 3 times more expensive.
sometimes seems the only way doing something as a hobby bit by bit is cheaper is because you don't see the whole bill at one time.
Again it'll be down to my lack of knowledge about machining but I had no idea from what I perceived to be the necessary work that the unit would take 3.5 hours for a professional.

Sorry if I annoyed you,thankyou for reply

Regards Ross

[sansbury]

You could always look for a fellow hobbyist with a more developed shop setup to help out. What you're looking for is not complicated and doesn't even need CNC to get it right-just a good mill and tooling and a steady hand with a ruler. A hobbyist also doesn't have to cover rent, employee overhead, investments in tooling and equipment, advertising, etc. There might very well be somebody out there who'd be delighted to help for $100 or even a good bottle of Scotch.