1020440S Cross Member Tubes

[aniljangra]

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
twist1.jpg

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.
twist2.jpg

Better pic below (with flash off on camera) showing the amount of twist
twist3.jpg

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

[tufanca]

The application was made friends mechmate miles? You can mail me at if? Thanks
talbistan@hotmail.com

[swatkins]

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...

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

[smreish]

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.

[Gerald D]

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 . . . . .

[swatkins]

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!

[Robert M]

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

[Gerald D]

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.

[KenC]

All tube available here bulge, will it be a problem?
Cross member tube buldge.jpg

[Gerald D]

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

[KenC]

Thanks.

[AuS MaDDoG]

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.

[Gerald D]

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