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Graham S
11-23-2004, 02:14 PM
Ok, anything for a laugh.

Thinking about the construction of my router base at the moment. I am going for a welded base of either aluminium of steel. I can weld steela bit but not ali and I can get either of them welded in the department however ali will take more setting up and the technician time is scarce enough without doing things for me so leaning to steel.

Anyway here are a few ideas. I got some inspiration from a book called "Design of Weldments" by Omer Blodgett. The book is really good and describes how machine bases and other structures of superior stiffness and rigidity than cast iron can be made by welding steel providing the correct structure is formed.

The basic way to get a really rigid box is to add gussets that run diagonally in a criss-cross nature. It seems that having these members at 45 degrees to the "box" is important and there is a great picture in the book of test structures showing this.

There is also mention of adding slots for fixing things to beds. This reduces the strength of the bed unless the individual sections of the bed are tied together some how.

Attached are a few possible methods of doing this, the u-channel one is much like the book, not as good as the gusset lattice but good. I am going for the one with the V channel (my own design), I think I can make this lighter than the other and just as stiff if not stiffer. I was going to make a stiff box and add aluminium t-slot material to the top but with this method I will end up with steel slots and also save some cash which I really need to do. The choice of V slot is based on availability, it makes the machining a tad tricky but not really that bad. I am not sure but I think the V may also be a bit stiffer.

Sorry to waffle, just thought I would start the ball rolling on this subject.

Cheers,

Graham

Graham S
11-23-2004, 02:16 PM
Oh, the big blocks on each end of the left most picture are to support my gantry rails (they may remain as beefy ali extrusion I already have).

Graham

marx911
11-23-2004, 02:36 PM
just curious .... you didnt mention the overall size of your table and I was thinking .... all the time and effort to weld up your table you will have a lot of heat in this and I'm not sure how flat it will be when you are done .... I looked at it and was thinking why not just make it out of solid stock Al or steel machine in your t-slots and be done? you would have a stiffer base with alot more meat to keep vibration and movement down ... just my thoughts

Mark

Graham S
11-23-2004, 04:22 PM
The base is 730X730mm

The cost of a solid base would be HUGE for equivalent stiffness, it needs to be very thick just to have enough meat for the t-slots. Then there is the weight, a solid block would be impossible to get into my attic where the machine will be kept and also increadably difficult to move about in general. I hope to make a base that is stiff because it is smart not just because it is fat :)

Indeed it will warp during the welding process and this is where I am glad to have access to a huge milling machine to skim the surface. If you are getting serious then I think the frame should also be normalized in an oven however I suspect that will not be needed.

Graham

WeCheat
11-23-2004, 10:49 PM
Have you ever thought of using Epoxy and stitch wielding it?? 3m make some epoxy for auto/air craft construction that we have used to make thin gauged parts that would warp very easily if wielded all the way. We Just glue it all together like wood, just not where the stitch wields will be. We get real good result with this method and it is very very strong. Most of your car roofs are done in this manner. You can get the stuff at the auto parts store. :cool:

Graham S
11-24-2004, 09:31 AM
What do you mean by stitch welding? Do you just mean intermitant short runs of weld?

ViperTX
11-24-2004, 11:20 AM
Graham S...use your approach...boxed members for structural integrity yet light in weight is cool.....more mass in the gantry section to minimize the effects of vibration is also good.

WeCheat
11-24-2004, 08:41 PM
What do you mean by stitch welding? Do you just mean intermitant short runs of weld?
Yes it will be very strong and have a lot less in the way of warping do to the low amount of heat put in to the part.

Graham S
11-25-2004, 06:13 AM
While talking to the guy who is going to weld it he mentioned stitch welding without my prompting, even without the glue it should work well. My book on weldment design also covers welding to minimize distortion, I think you essentially go around tacking opposite corners and allow the structure that provides the eventual stiffness to prevent the distortion. The opposite corner thing is also a little like tightening the bolts on a cylinder head, sort of balancing the forces.

Anyway I have rough cut the steel, I get the plate for the top (which will be slotted after welding) tommorow, I now need to size the flats accurately and set to the task of making all of those V slots :O

Graham S
11-25-2004, 04:42 PM
Steel now sized and the central slots that allow the diagonals to interlock are cut, marked out all the other slots. Started to make a little template for hastle free marking of all those Vs.

JavaDog
11-26-2004, 09:29 AM
Steel now sized and the central slots that allow the diagonals to interlock are cut, marked out all the other slots. Started to make a little template for hastle free marking of all those Vs.

Pictures? :p

Graham S
11-27-2004, 07:34 PM
Will do, should have something worth picturing on tuesday.

Collected the steel plate that will form the bed itself, it is 730mm X 730mm and 6mm thick, that's 28"X28"X1/4". I assumed being quite thick and expensive that it might be flat, oh well... There was a 3mm box in both directions and one corner even seemed to be turned over slightly. I have managed to get it a lot flatter by bending it on a fly press but it is still far from perfect. I don't want to clamp it flat for the frame to be welded to it as it will just build in stress, I can't mill both sides unless I want a 1mm thick piece of metal at the end that cost X6 as much as it should either.

So I am going to build the reinforcing framework seperately, plonk the sheet on it and weld it, the weld will have to fill the gaps and epoxy could also be used as suggested earlier. Then after the final surface machining I should still have enough material left for a bed.

Graham

Graham S
11-29-2004, 02:22 PM
Here are the pictures as promised, it didn't take long to make the vertical slots so that the main uprights slotted together (although I did break a couple of 2mm endmills) but when I realized there were 36 V shaped slots in them to cut I was a little worried. Turned out that the marking out took no time at all with the little steel template I made and the cutting not much longer on the band saw. I have never cut steel on the band saw before and although noisey I could keep to my scribed lines easily, more than good enough for the slots. In theory of course the Vs should be cut at a slant but rather than do this I cut them so they are more like an extended V, anyway they are just two simple cuts each.

The angle has not also been cleaned up, on the faces to be welded using a linisher and in the channel with just a wire brush to remove the rust in case I get the thing powder coated or paint it.

Hope to get our cheif welder to weld this tommorow, he is going to do the outer square first, then I will make sure everything fits and he will weld up this frame inverted to how it is now on a flat table. Then the wonky plate can be added.

Cheers,

Graham

JavaDog
11-30-2004, 08:38 AM
Here are the pictures as promised
Cheers,

Graham

That is coming out really nice! What do you estimate the total cost on this is going to be?

Graham S
11-30-2004, 12:56 PM
The frame as you see it was about 40GBP (at the university stores price which adds 10%), bear in mind that the current exchange rate will make that seem a fortune. It is 6mm thick steel for the outer and then 3mm thick for the inner structure, 60mm deep. In the US I bet it wouldn't cost much. The 6mm thick plate to go on top is about 45GBP.

The frame as it is seen above was inverted on a welding table and tack welded all over, then we allowed it to cool and some more substantional welds were done. It has not deformed and still sits flat on the table. Leaving the rest of the welding until tomorrow. I then have to put Vs in the end plates to allow nuts to be inserted when in use, this will just be done with a hacksaw and "finger" handheld belt sander.

Rather pleased with it so far, as it stands it is seriously stiff and very easy to move around, the frame weighs less than the plate that will go on top of it.

Graham

Graham S
12-09-2004, 03:44 PM
Trials and tribulations of a steel bed:

Well I returned to the workshop the next day and the guy doing the welding had got stuck in, it seems he decided it was well tacked up and heat no longer mattered. Well the result was a distorted frame, there was a 5mm bow in the middle. After removing myself from the ceiling I decided to assess the damage. Welding the plate to it as is would be no good as the gaps would need lots of weld to fill them and even more heat!

So I tacked on some lengths of angle allowing the bed to be clamped onto the big mill and machined the top, taking off about 2mm. The bow went right out to the corners and I soon had a lot of contact between the plate and frame when trial fitted.

I also had another go at the plate, I realized most of the problem was in one corner, probably due to guillotine cutting. This was "adjusted" with a sledge hammer, leaving a pretty flat plate.

I then welded the plate to the bed. Even though I have not done much welding in the past I did this myself using very short stitch welds and lots of time inbetween for cooling, I also spread them around doing opposite corners etc. This process took me about 3 hours and I couldn't stop for a break as I was working out of hours and would be chucked out soon, anyway the result was a well held top plate and no distortion, well not much, about 0.5mm up at one corner.

I then sent the whole thing in for normalization (cost 20GBP cash in hand) and got it back this morning. I have started cutting the slots (6 more to go) and hope to have it all done including the final skimming on Monday or Tuesday.

Then it needs some finishing, power coating or just paint perhaps, not sure yet.

In the end I think the bed will kick ass but I wish I had just learnt to weld at the start. You need to really pace the welding and be able to leave it.

Sorry no pictures, I was too upset (this whole saga lasted most of last week).

Cheers,

Graham

JavaDog
12-11-2004, 11:15 AM
Sounds like the final result will be worth the headache.

Graham S
12-13-2004, 02:07 PM
After the slots were cut. I had to rotate the bed by 90degrees to do it. Took forever.

Spot the "deliberate" mistake. Or rather what I forgot to do before adding the plate.

ViperTX
12-13-2004, 03:26 PM
Graham S,
That is one huge milling machine. Boy, acess to one like that would be great!

Graham S
12-13-2004, 03:47 PM
It is a monster, I'll post some more pics later. All three axis and the rotary table are on a DRO and also powered. The spindle is also pretty good going upto 1800rpm and down to 30 or so. To be honest I feel a bit guilty using such facilities, it is hardly home CNC if you need a mill that size. Some of the cutters are also the size of dinner plates, taking about 20 inserts!

It is now partially skimmed, should be a picture of that tommorow once finished, using a smaller shell mill with inserts.

Graham

Graham S
12-14-2004, 02:06 PM
now ready for the finishing pass. Had to take about 2.3mm off it to get to clean steel all over. Note the spot where I hit the stop button by mistake.

ViperTX
12-14-2004, 03:12 PM
Looks purdy!!!