1020440S Cross Member Tubes
 

In this thread we can talk about:
- what if 100x50 box section is not available?
- can the wall thickness be thicker or thinner?
- how long must the tubes be to replace a SB gantry?
- what if they are not cut square?
- etc. Anything to do with the selection of material, size, shape of cutting the cross tubes/members.

I'm about to get these cut for my Y Gantry. Is my reading the plans correct, that the beems should be 500mm longer than the max size of the workpiece I'm going to use in the machine..???

I mean, if the max board size is 1220*2440 mm the I need to make the Y-size 500 mm longer, ia. 1720mm and the X lenght is going to be 3040mm long right..??????

Yes, the drawing 102044S is correct. This how the 500mm is used:..............

1. the center of the cutter must be able to move further than the edge of the board because you often use the side of a cutter to cut the edge. Allowing the center of the cutter to move 50mm past on all sides adds 100mm to the beams.

2. The wheels of the car riding on the gantry must not fall off the ends of the rails. The distance between the Y-car wheels is 381mm and so we need to add that to the 100mm above.

Total 481mm. Using 500mm then leaves less than 10mm tolerance on each end.

(for the x-rails the distance between the gantry's wheels is 475mm leaving 12.5mm tolerance each end)

1020440S Cross Member Tubes
 

Gerald,

I got a great deal on 2"x4"X1/4" tube at the local scrap yard. Do you think this will be too heavy for the cross member tubes in the gantry or will it be okay? I priced new 1/8" stock at a local supplier and he wants $120. Yeow!

Doug

A heavy gantry means that the machine must slow down a lot before it can take a sharp corner. I think that the 1/4" will be too heavy.

Hi friends.. the cut of mine 100x50 pipes are not realy square... on the afternoon I can post some pics. My doubt is:
What`s the square tolerance to this cuts?

Leandro

Look at Note 2 on the drawing for cutting the tubes

100 x 50 mm tubes
 

Gerald

I want to cut 1525mm ( 60 in ). So my tubes should be 1525 + 500 = 2025 mm long, is this correct? Sorry for the dumb question. I'm getting the metal as soon as the roads clear up enough to pull a trailer on safely. It only takes a few inches of snow and the Pacific North West Coast shuts down.

Dave

That's what the drawing says.

Hey Guys - Local steel supplier doesn't have 14 gauge for the gantry tube - can I move to 11 gauge and still be okay? - Not much weight difference.

Sounds okay, but I am not familiar with gauge sizes. The tube can be 2-3mm wall thickness. You might have to drop your acceleration setting for heavier metal.

Gerald and Jeff.
I used 2 different wall sizes mentioned in both machines. 11 gauge on mine and 3/16" wall on Nils machines. The added weight & mass, using the geared motors, has not been noticed. The 11 gauge, which is 1/8" thickness, is a little easier to weld to. The 3/16 wall on Nils machine was really nice because I was able to tap his Tube members and not use the clamping strip internally. Lot's of choices, all worked on our builds.

If your using direct drive motors, I would highly recommend using the specified tube. The extra mass on the thicker cross tube members is noticeable.

Sean

Also, for a 1220mm [4 ft] Y-dimension, the bit of extra mass is less significant than on a 1830 [6ft] Y-dimension.

tube thickness
 

I don't want to be the dope here(to late) but where is the thickness of the gantry spec in the plans.


MAC

re. tube thickness
 

10 20 440 !!!!!

The wall thickness is hidden away in these two places:

Cross Member Tube Length
 

I have become stuck on the cross member tube. Instead of using the normal steel I have used square tubing for the main beams and most of the formulas will not work. My overall outside main beam outside to outside length is 1952.625. I have looked throw the plans using the formula 1010300 to make sure of Y figure. The Y length is 1522.625mm using this formula. Now using the formula from 1020440S I have added 500mm to my Y length and have came up with 2022.625mm. When I cut the tube to length I have 25.4mm over hang on the outside of the x-rails. Is overhang length correct? I would like some input before welding the Gantry Frame.

Thanks, Bryan

Are you sure you mean x-rails? (Not the beams?)
Is that overhang equal each side?
Is that overhang to the tip of the beam? (Inside the gantry it will be less)

Have gotten to my drawings now . . .

Your rail should overhang the beam by about 21mm

The tube should overhang the beam by about 34mm and overhang the rail by 13mm

Cross Member Tube Length
 

Gerald thank you for your assistance.

Bryan:)

Im a bit confused on these tubes, why are tubes needed for this?

I was thinking about getting precisionwelded profiles that are 100x50x2-3mm

What does a "precisionwelded profile" look like?

like a regular profile I'd say, just the non-rounded corners, and they are like super-awesome in precision :)

Is radius of the cornerns needed somehow? Since not many other parts have them

I think Frallen is refering to cold rolled steel tubing, greater precision and greater cost but no better strength wise than normal hot rolled steel and for this application the super awesome precision is overkill, but it will work.

So the "tubes" can be perfectly rectangular? or they need to be rounded?
Thats my main issue atm :)

They do not need to be rounded. But you will then need to file out the inside corners of 1020451 and 1020452 where the tube corners will touch.

Ahh great, i can get rounded ones, but I thought it was more to it that what you just wrote. So its all clear now.

100x50 twist. Just got my steel and one tube is twisted slightly. Anyone experienced this before?

My tubes were twisted but as the assembly is done upside down, either the center or two edges of tube were parallel providing reference surface for rails when turned around, other small gap is filled up with shims. I think it wont matter but I had no option anyway. I'll post closeup pictures when I am home.

Any luck with those Pics? I'm thinking a sharp twist back may help my cause.

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)