Sorry Besser, I nearly forgot about the pics as I was struggling with aligning rails on those tubes. Here are the pics showing twist, the fist one shows one edge parallel to stiffner and no gap between rail and tube
Attachment 7719

Next one is the other edge of same side, showing the gap between rail and tube, also notice that tube edge is not parallel to stiffner.
Attachment 7720

Better pic below (with flash off on camera) showing the amount of twist :eek:
Attachment 7721

I am thinking of laying some welds where the temporary washers are, on the tubes and grinding off.

The application was made friends mechmate miles? You can mail me at if? Thanks
[email protected]

Today I was at the steel suppliers and they were out of the 4" x 2" x .125 wall thickness... So.... I thought that more weight would make a better machine and splurged on the 4 x 2 x .25 tubing... :D

Then tonight I read where it might be too heavy :(

I plan on using a belt drive for the motors and a 50" Y width... Has anyone had good results or should I just go ahead and find the light weight tubing?

Steve

Steve,
I used 2 x 3 .25 wall on my second machine and have not noticed a bit of trouble with the added mass of the gantry. 7.2 geared motors, 30T pinions, 56vdc G203 drives.

Plus, the wall thickness allowed for me to tap the rail holes instead of using a clamp strip.

When I started this CNC lark, it had been totally drummed into me that lighter is better. Fortunately, I had a background in metalworking machines and my experience there was the heavier the better. So I loaded some ballast on the Shopbot to see what went wrong when it got heavier, suspecting that the motors would loose steps or something like that. Well, basically nothing went wrong and from then on the MM went in the opposite direction to all other DIY machine plans . . . . .

I had to pick up some metal for another project today and the metal yard had the correct tubing in stock... I decided to go ahead and stick to the plans, why mess with a known winner! :)

Gerald,
Unfortunately for me, like some, the metal suppliers I contacted then, all had NO stock on that gauge, std around here is 0.120” !
If I remember correctly, and please correct me if I have either Alzheimer’s or delusional thoughts, haven’t I read heavier tubing in our case, for gantry or I believe even other moving parts my motors, is not really desirable !
Doesn’t it put more unnecessary strain & “moving time” on the motion to either start or stop this motion !?
Robert ;)

The distance required before you reach full speed is increased if you want to keep the same torque on the motor and not overload it. Therefore, if the mass is increased, the motor's acceleration and deceleration values (times/distances) must be increased. In reality we saw very little change to the motor tuning for quite big mass. With the Shopbot, we had high flexibility and had to have low acceleration for that - with the greater mass came greater stiffness and nothing really changed in the motor tuning.

All tube available here bulge, will it be a problem?
Attachment 8352

No, that is not a problem. Just be careful to keep the rail surface flat (relative to opposite rail)

Thanks.

Hi All,

My Gantry beams are 100 x 50 x 3mm thick, would I still be better to add the metal backing strip drilled and tapped or would I get away with drilling and tapping the 3mm thick RHS ??

Thanks
Tony.

Do a test hole and see if you can really tighten a screw in there before it strips.

hi .. iam collecting parts but i found beams of 5mm thick almost free. they are heavy 10kilograms per meter while 3mm thick is 6.60 kilograms per meter.
what do you think? the inertia will be more but the resistense will increase. UNBENDABLE
http://mimg.ugo.com/201108/8/4/9/206...528_poster.jpg

If you accept that the inertia is higher (less acceleration) then it should be good. If you have geared/belt reduction motors, you might not notice any drop in acceleration. With direct-drive motors I will be slightly nervous, but my stomach says it is still going to be good. Nobody has yet complained that their MM gantries are too heavy - it is not a point of discussion yet.

Mechmates are to heavy (just wanted to be the first)

Maybe your floor is too weak?

...Funny, I found myself astounded at the simplicity and lightweight nature of the MM. I have owned many CNC machine's in my lifetime, and they usually require an entire team, forklift, heavy lifting equipment to move or even assemble.

My particular 5x10 MM, was built, moved and moved again by myself and a mate with no special needs or additional cost. A Bakkie and a trailer was all that was needed both times.

Not sure I agree with your statement "MM are to heavy"

Hey Sean, you have Bakkies in the States, thought you only had trucks there? :D

Oh, and I think Besser was just trying to get a rise out of somebody...

Lets be specific.
MM is too heavy for 2 fingers to lift. :D
Too heavy to float on water.
Too heavy to for transporting with bicycle without a bakkie.
Too heavy to balance on my head...

Definitely too heavy for this mode of transport
Transportation

You remind me of this one http://www.youtube.com/watch?v=_8HyTyTbS5A

That is amazing. It is amazing that he could get them stacked that high and then to be able to walk away with out dropping them.

When I was stationed in Korea in the 80's the craziest thing I saw was 5-6 people on a bicycle or cages of live chickens stacked 8-9 high on the back of a bicycle and best yet a washing machine on the back of a bicycle. And that was in downtown Seoul.

I guess my question whether .188 thick tube would be too heavy has been answered. Thanks to all who have gone before me, may the force be with you.