[j.smith]

Well, I guess it's time to get this build thread started as we are a good way along on the table.

After looking at the Mechmate, Shopbot, and various 8020 builds we decided to go with a welded steel table and gantry. I wanted a stiff machine that could run at high speeds and aggresive cut depths. We will initially be using it for mostly cabinet work but did not want to be excluded from working with denser materials as we got more familiar with the tools capabilities.

Looking at the 8020 designs there just did not seem to be enough mass to control the forces of a large gantry working at high speeds. When finished, this build will weigh in around 750 lbs, which should be good to minimize the effects of the moving gantry and produce good clean cuts.

We started building thinking the table would be 48 x 96, but ended up at 66 x 120 so that we could work with 5 x 8 sheets of baltic birch; the cost difference in he raw materials to increase the size was minimal.

Just to set the bar, this is being built by my son and I (he is doing most of the manual labor, I am provding moral, monetary, design support). We both are familiar with welding and metal work, but are no more than weekend warriors at it.

So here we go...

I bought the Mechmate plans and spent a lot of time pouring over them, it closely resembles the Shopbot PRT style of router and the more I looked, the more I realized I wanted the more modern PRS style raised gantry. I looked at buying a Shopbot PRS and came to the conclusion that we would quickly be in the $20k range to get a working system; so I sat down with Turbocad and started drawing lines and sticking them together.

I decided to use 2x2 square tube and 2x6 rectangular tube for the X axis and gantry Y axis, mostly because it was readily available and relatively inexpensive. I chose to use 11 ga steel with the intention of using threaded inserts instead of tapping the bazillion holes where threads would be required (this saved a bit in material costs as it would have required the use of 1/4" steel to have enough meat to thread all of those holes).

So we bought 100' of 2x2 tube and 40' of 2x6 tube and started cutting....

[j.smith]

Once all of the parts for the legs and table were cut it was time to start sticking them all together. Initially we were going to assemble the legs using braces from the center to the lower part of the legs for support, then it hit me that there was going to be a lot of wasted space underneath the table that could be put to good use as storage for sheet goods, so the design was updated to include two shelves for 4x8 sheets or whatever waiting to be routed.

Since neither of us were professional welders we stacked the deck in in our favor as much as possible with tools and aids to make the assembly easier. One concern we had from the start was keeping the steel square and preventing it from pulling while welding it together. The combination of the material selected and use of some heavy duty welding clamps from Northern Tool kept everything square throughout the assembly process. In the picture attached you can see the heavy green welding clamps - best $49 (per clamp) spent so far on this project. As we go along it becomes apparent that the most expensive part of this build was all of the additional tools required ...

So the legs were finished first, then on to the table ...

[CarveOne]

I'm glad to see a resurgence of steel builds around here. For a while it seemed like I was bucking the trend with my two steel machine builds. But I'm just that way.

Keep on welding.....

CarveOne

[j.smith]

The table went together in the same fashion as the legs, but, it became apparent at this point that the 2x6 tube was not straight from end to end. The difference between the center and ends was on the order of 1/8". We took a short time out to reconsider the choice of materials and breifly considered changing the X axis rail to 3060 aluminum extrusion until I received the quote for the material. At $3 per inch for the aluminum extrusion I knew we would find a way to make the steel work ... so we continued welding ...

About this time we started working on parts for the gantry and the next tool requirement surfaced. It turns out that it is not possible to manufacture the gantry supports or guide blocks for installing the rails for the linear carriages wihout a mill (that's my story and I'm sticking to it)... So I gathered up the keeper of the checkbook and took her on a trip to beautiful Missouri, home of Grizzley...

[j.smith]

We welded and welded and the next thing you know we had a table with legs and cross supports that weighed in excess of 500 lbs, seems I neglected to consider how we were going to move it once we started to get the major assemblies welded together, so... four 5/8" holes and another trip to Northern Tool solved the mobility problem; add a little Safety Blue Rustoleum and it is starting to look like something...

[kiwibrick]

Wow, 1/8" is quite a bow in 3.0m!
I guess I was lucky to get both my main rails (100x75 or 4x3) straight to within 0.2mm over 2.0m from the shop.

[j.smith]

Which brings us to the present....

Now that the table is assembled and protected it was time to deal with the hump or crown or whatever you want to call it in the X rails. I had always intended to use a leveling compound on the top of the X rails since the tube normally has a cup in it from the forming process, and I was prepared for some discontinuity in along the length which could also be resolved using some sort of self leveling, low viscosity material. I was not sure exactly what we were going to use at the start but hey - Google knows everything, right??

Well, the search for a low viscosity, self leveling, hard curing compound turned out to be more involved that I had expected, there is some steel impregnated material made by LocTite for industrial use only and which must be mostly gold because it would have been cheaper to go back with the 3060 than this compound... Then I noticed where the canuck was using West System Epoxy, now why didn't I think of that??... I watched his progress and was a little dismayed when his initial pour was not as he had expected, so I sent an email to West Systems explaining what I wanted to do. The reply I got indicated that their epoxy should work fine but I should use the 209 Extra Slow Hardener to allow the epoxy the maximum time to flow and level out. Canuck had used the 206 hardener, the 209 has a pot life of 50 minutes and thin film cure of 3 - 4 hours. So we installed the thread inserts, leveled the table and built a dam around the X rail and poured....

It took 20oz of epoxy per rail resulting in a continuous shim the entire length of the 2x6 tube. Since it is still curing I cannot provide an accurate measurement, but at it's thinnest it should be around 1/16", at it thickest around 1/4". both sides have been poured and the results at present are very encouraging. I plan to let it continue to cure for another 2 - 3 days before messing with it but the surface is smooth and appears to be level from end to end and side to side. There are a few bubbles that will require some work and the edges will require some cleanup but I do not expect to have to mess with the surface of the epoxy.

[giz]

Great work and documentation so far. Have you thought about how you might deal with any height difference in the epoxy surfaces? You could probably shim the gantry if needed.

I think your welding looks great!

[Jkountz]

This is one I will be watching with great interest. I am currently working on the design of a very similar built but in a 4x4 size. I was shocked to hear of the bend in your x axis, thats extreme in my experience but you solution seems to have worked in leveling the rails. I too am curious as to how you will go about making the sides the same height now. I was thinking of using C channel instead of rectangle tubing so I could mount my R&P rack to the underside of the C channel. Also I thought it would provide plenty of stiffness and yet save a few pounds of overall weight and cost. Still working on that one though. I have attached a rough Sketchup drawing of what I have done so far.

[PaulRowntree]

What did you use as a release coating for the bolts in the epoxy?

[j.smith]

... Have you thought about how you might deal with any height difference in the epoxy surfaces? You could probably shim the gantry if needed...

Any height difference should be small and we will deal with them by adjusting the gantry supports. The first side poured cleaned up very nice last night, we did end up sanding the entire length of the rail though. Will be pulling the other side mould down tonight and we'll see where we are.

... What did you use as a release coating for the bolts in the epoxy? ...

A light coat of trailer wheel bearing grease, probbably could use any lubricant that will not wash away when the epoxy flows around it

... I was thinking of using C channel instead of rectangle tubing so I could mount my R&P rack to the underside of the C channel. ...

Yea, hindsight being 20/20 I would probably increase the thickness of the 2x6 tube or switch to C channel. The Mechmate is built using C channel and seems to be a pretty sucessful design.


I'll post some more pictures of the rails and shim tomorrow after we get the second side cleaned up

[Jkountz]

Any more progress on this build? You've got us all hanging here!! LOL

[gaza]

just posting into watch this build

so will you still shim your rail to a set height now that you have a flat surface from the epoxy

[j.smith]

...so will you still shim your rail to a set height now that you have a flat surface from the epoxy

Actually it looks like the two surfaces are within .005" of each other so I will adjust the gantry beam as required to get everything level.


Sorry it took so long to get back, the West system epoxy with the 209 hardener worked great, I now have a continuous level surface on both X axis rails. I did end up sanding the surfaces, not so much to adjust the thickness but to get each one flat. As the epoxy flowed to level the surface it left a small lip where it was in contact with the dam used to retain it in place. A couple of minutes with a small block plane and sanding pad and it was perfect.

Since my last post I have installed the 1/4 x 3 steel rails for the X axis and assembled the carriages which the gantry will mount on. I had to take a time out to upgrade my mill with a DRO so that I could make the rack clamps for the R&P drive systems. I have also received my R&P drives from CNC Router Parts and have them installed. I have a 72" length of rack for the Y Axis and will be installing the inserts and fitchecking the rack and drive system next while I wait for the 120" racks from Moore Gear.

The gantry is going together, the uprights are done, just need to weld them to the top plate for the linear carriages, the arrangement is shown in the pictures below.

Next thing I need to decide is what motors I am going to install on this beast and am open to any input. I was originally planning on using the NEMA 34 motor kit from CNCRP but in all of the reading I have been doing on the subject it sounds like I don't need that much horsepower (960 oz in on the X&Y, 640 on the Z), so I am leaning towards Kellings 570 oz in NEMA 23 motors. My best estimate on the final gantry weight is ~85 lbs. There is a huge cost savings in the NEMA 23 motors over the NEMA 34's. Anyone got any wisdom to share???

So below are the pictures of the build so far, sorry it took so long...

[m.marino]

It depends,

I am using Nema23's at 3.1Nm (appox' 439 Oz in) and I am moving a 30 kilo gantry with two of them direct mounted. I also have them on the Y and Z axis and they more then do the job.

Big advantage of Nema 23's over the 34's is reduced enertia from the motor itself. Then you have to look at and reduction you might do which can have a big effect on how much torque you have available.

Michael

[freecncplans]

This is for my machines, which is aluminum and not welded.

The Gecko 540 and Nema 23 setup ran about 700 IPM rapids and cutting was sketchy for speed and cutting depth. The Nema 34 setup runs 2,000 IPM rapids and cutting is limited by my router for my machines.

Sean