En nog eens De Vliegende Hollander, natuurlijk:
Attachment 11545
Attachment 11546
Attachment 11547

ok...now that's funny. I needed that levity today!
Cheers.

BIMA you say? Here's one for $88,000.

Looks almost to scale! :)

Heel leuk!

I always wonder how many people of Dutch origin are living around the world? Must be more than the total population of Holland.

Grappig

is inderdaad leuk, ook om wat nederlands te zien

Zeker zie ik hier Nederlanders van allerlei landen... maar niet van Nederland zelf?! Moeten wij ons maar bovenlanders noemen?

Jawel hoor, ook van Nederland. :D

Sascha, hebt je naam "skillalot" iets te doen met piepers jassen?

(Trying to un-hijack this thread from the Dutchmen...) Jan and Sascha are now talking about "piepers jassen" which means peeling potatoes. The 'guy' way to do this is impaling the spud on a quarter inch drill bit and spinning it near a pocketknife. Surely a MM would do a better job on this, or other repetitive culinary tasks?

Nee, niks met piepers schillen hahaha.

Terug on topic dan maar.

Work is progressing on aligning the rails. I built an "alignment car" in the same style as some others here, to make this process easier.

The distance between the V wheels is the same as the bolt spacing. I used a 10-lb lead scuba-diving weight to balance and steady the car. It was still tending to hit the legs of the table, so I added some weight (the step blocks) on top.

The laser is held in place with elastic bands, and is positioned directly over the V to minimize any vertical motion of the laser if the car swings sideways.

The rail off-cuts clamped at the end are for preliminary alignment of the rails, using a fishing line.

Now, what does the laser point at? The door of the workshop, which is 3.5m from the near end of the rails, 9m away from the far end.

I printed off a sheet of custom metric graph paper to act as a backdrop for the laser dot. This was checked against a known-good ruler, to make sure my printer actually printed the dimensions correctly.

The car was positioned at the bolt boundaries (1-2, 2-3, etc) and a photo taken of the graph paper with laser dot, with a handwritten label to identify the car position. Later, I compared the photos on my computer to measure the offsets from one position to the next. These were used to calculate the required shim thicknesses.

Melissa,

Nice explanation of the "alignment car" and the procedure. The pictures help immensely.

So after using the "fishing line" to get your initial alignment, how much variation did you measure using the "alignment car'? I would also be interested in how much variation you measure with the "alignment car" after you shim.

I used the fishing line for lateral adjustment only. I used the car for vertical adjustment.

The weird part is that my baseline measurements show a maximum variance of 0.25mm on the Xa rail. (I'm calling the rail closest to 0,0 "Xa". The other rail I'm calling "Xb").

Now after shimming, I'm calculating a max variance of 0.45mm, but with fewer peaks and valleys. I don't know... maybe my math is off, maybe I'm just going crosseyed from staring at spreadsheets :confused:.

At any rate, the laser dot wiggles around much less when I roll the car down the track now.

I didn't find much on the forums about what tolerances others are shimming the rails to. What's typical? Is 0.45mm (about 20 thou) good enough? I can already picture Gerald rolling his eyes... :).

:eek:

:D

I spent a week and a half chasing .015, in the end I cant tell the difference. Just get it going, the fun stuff just begun ;)

Tim
Still climbing the learning curve

Think about:

The gantry rides on a couple of rollers, so it takes a average/smoothed height

You "surface" the table to follow the rails

The material that you are cutting is mostly thin and bends to follow the table surface

For thick materials, what will you be cutting that needs a perfectly flat surface?

I did not even SHIM my rails...bolted the rail on the C-channel, surfacd the table, surfaced the sacrifice board and happily cutting for a while now without any problem.

Kobus,
No shimming at all? I was sure you would take the opportunity to use up some rum and cola? :)

His rum is in a glass bottle and his cola in plastic - real classy guy from around Charlize Theron's original hangout. ;)

I am a straight and level guy...:rolleyes:

Wanna hear a little secret? MM #5 has no shims either. I aligned everything laterally, and left the vertical to chance - It actually worked out fine for the first year in production. When I moved the machine I did shim just a little, but nothing serious.

All those pictures of really nice acrylic and such cut, were from the original setup! I guess when you have a great design - everything works like it's supposed to. :)
Sean

After over a year operating mine, I regrated spending so much time on shimming...
I recon with a good vacuum hold down, all sheet stock will trun out as true as the surfaced spoil board.

My major aim in getting the rails reasonably level is so that the 4 rollers of the gantry share the load evenly, but the bit of twist flex of the gantry mostly takes care of that.

This may be off topic but while we are at it, what will happen if we increase the height of the gantry by lengthening 1020456?

To keep the 4 rollers equally loaded, eventually you'd have to increase the 'wheelbase', or reduce the speed? Think of the 'weight transfer' (as the racers call it) of a topheavy SUV braking or accelerating hard.

SUV don't have a spring to hold it on the road...

True, but there's also the issue of lateral forces (along Y). If 1020456 is taller, then 1020451 and 1020452 need to be taller to match. That may induce flex between the gantry tubes and the wheels, and require making 1020451+2 out of thicker steel, or perhaps adding stiffening ribs (along with the resulting weld distortion).

I'm not an engineer, so I haven't (and won't) calculate all the possible forces here. But it's important to remember that it's a system of parts, and changing one part can have many side effects.

Springs (or rear spoilers) holding it down are secondary. If where the drive force is applied is low (near the road or the table), and the center of mass is high, then any acceleration induces a torque about the center of mass, just like pulling on the top of the gantry would. That torque changes the loading on the wheels. The bigger the lever arm for that torque (the taller the gantry, or the shorter the wheelbase), the stronger the effect. Build one out of lego if you still doubt this.

(I trust Gerald that equally loaded rollers actually matters.)

Under cutting conditions the rollers will not have equal loads. But we have to try our best to get even or balanced loads. What I am trying to say is that we don't want a roller to lose pressure contact with the rail, because then the stiffness of the whole machine suffers.

Interesting...
Unfortunately, it is not easy to determine the cutting force acting on the gantry. This just lead to a dead end. :(
For all I want to do is that extra 50mm or so of extra gantry clearance, maybe its too much to ask.

Ken, remember that if you lift the gantry up 50mm, then the z-slide has to extend 50mm more from the Y-car (for cutting the same job).

That is true, but what if I don't venture into that extra extension?
If I have a thicker table board, with vacuum plenum on it + bleeder board. That extra 50mm clearance will come in handy. & at most I'll extend another 25mm...
From that an additional 20~35mm extra extension. Not really a lot... I hope...

I don't think it is a lot either.

A little bird told me that in a few hours the rails will be straight to within 7 thou, vertically and laterally.

...and at the cutting tool bit that is almost undefinable. Great work.
Sean

A couple of photos of the shim procedure -- cards and Guinness :).

The paper cutter came in very handy, especially for the spots that needed multiple card thicknesses. It uses cutting wheels, and one can make a perforated cut. That's ideal for folding the cards, without the usual bump that results from folding something this thick.

The gantry is now rolling on the rails :).

It's NOT rolling well :mad:.

I've got about 1mm of diagonal wobble (propellor twist). I tried bending it down against the table, as Robert M did in his build thread. I ran out of thread on my clamps before I got it bent far enough to make a difference.

Next attempt: pull up instead, using my gantry crane. I clamped three corners to the table, and used the crane to lift the fourth corner to twist the gantry the other way. Didn't work... I ended up lifting two legs of the table clear into the air :(.

The other headache is that the rollers are not contacting equally along the length of the table. I have more wobble at one end than the other. Hmph.

Any suggestions?