Mark's EPOXY Granite 18"x20"x20" (700mmx780mmx780mm) vertical mill build

[gt40]

Update:

I was able to rent a giant hoist for cheap and flipped the base and went to work removing the mold material. I even managed to alarm the wife dangling a 700 lb block over our driveway

I was really concerned whether all the work to use ground steel plates and pre-drill the mounting holes for the rails would be messed up by the epoxy. Good news, rails bolted up on a test fit and without even trying, are only .0242" off over the full length before even starting- casting does not seem to move ground steel plates. I had previously aligned things with a granite surface plate between the ground steel bars. It is a lot easier to mount things before you pour...

Couple of quick pics before I clean everything up this weekend.

I am happy things fit and the alignment works. Hopefully it will start to make sense because up till now, everything has been upside down for casting purposes...

3 foot base for the linear rail:



Mill base with servo and ballscrew sub bases + rail mounts:


Test fit:

[daniellyall]

all can be said is well done

[pippin88]

Do those rails sit proud of the epoxy (just thinking it will be easier to grind or scrape)?

Nice work

[RotarySMP]

700lb is a lot of mass. Did your vibrator still move that as the last batches were going in?

[gt40]

Do those rails sit proud of the epoxy (just thinking it will be easier to grind or scrape)?

Nice work

The ground steel bars are flush and the epoxy granite doesn't protrude. Based upon indicating the bar yesterday, I don't think I will need to scrape at all.

Here is another pic:

700lb is a lot of mass. Did your vibrator still move that as the last batches were going in?

The vibrator shook pretty strongly but I wish I had bolted at least one more to the other side. There were no significant voids on the entire piece so it worked partially. I was also trying to go for the lowest level of epoxy I could get away with. 2-4 bench grinders bolted to each side with eccentric weights would be the way I would do it next time...

[mcphill]

How did you get such precise positioning of the inserts prior to the pour? I assume that was done at this point, right:



I would think the melamine/particle board would not provide enough stability to hold the parts in a .001" tolerance over too long a distance, is that not correct? Or did you clamp them to ground gauge blocks to keep them a precise distance apart? Or ???

Looks great, just trying to think of how to do mine...

[gt40]

How did you get such precise positioning of the inserts prior to the pour? I assume that was done at this point, right:



I would think the melamine/particle board would not provide enough stability to hold the parts in a .001" tolerance over too long a distance, is that not correct? Or did you clamp them to ground gauge blocks to keep them a precise distance apart? Or ???

Looks great, just trying to think of how to do mine...

I through bolted 1 ground steel bar to the melamine board with coupling nuts and bolts. Then I used a verified square granite surface plate and aligned the other ground steel plate to that, prior to bolting.

As you might surmise from the above pic, I started loose and then moved the granite from one end to maintain the same distance from the first keeping it tight to one side. Kind of a giant heavy witness block. After I was done, you could slide the granite surface plate from one end to the other with zero gaps and both steel plates parallel as a result. Bolting the melamine to the ground steel bars every 80mm/3.14" keeps everything pretty straight and the steel bars are 3" wide. I was going to bolt precision ground stock as crossmembers to keep it aligned but after indicating the 2 bars bolted to the melamine, I didn't need to- the epoxy granite will hold everything anyway. Hope that helps

[mcphill]

Hope that helps

Certainly does, thanks!

[gt40]

I forgot to mention do the alignment with the melamine on a flat surface before you tighten the steel plates down

[ger21]

How flat are the bars? Melamine is rarely flat.

[gt40]

The bars are precision ground to .001" on all sides and are 1/2"x3"x36" O-1 from Starrett.

[G59]

Instead of bench grinders, you could of used a couple of orbital sanders mounted to the bottom of your mold. Contrary to what most think, you don't need a large offset mass to create strong vibrations. A lot of it has to do with the frequency of the vibration.

I wish I had the time to test this out in the real world, but I would mount two palm sanders on the bottom and have them turned on the minute the epoxy is poured in. Once the mold is filled, vibrate for an additional 5 minutes and then I would run a palm sander over each side of the mold for a few more minutes.

On another note, I like the look and color of your mill's base. This is the biggest one I've seen on the forum and I hope everything turns out as you planned.
The bar stock idea seems to have worked, I'm just not sure if repeatability can be had that way.
Keep up the great work.

[rocketflier]

How flat are the bars? Melamine is rarely flat.

With 700lbs, it's the shape of what it's sitting on.

[gt40]

Update:

I got everything de-molded and was able to test fit the linear rails. I was able to indicate them parallel to 5 decimal places and about 7 thousands variance on height so the ground steel inserts worked as a design element. I will shim and grout for the final install but sweeping the full length of the ground steel bar embedded in the base measured only .007" height difference. Interestingly, my linear rail has some variance independent of this also.

Here are a couple of pics. I had only one significant void on the corner that was noteworthy and only cosmetic. The base is fully functional and bomb proof.





It was a real pain to remove all the molding material- a few moments spent with mold release would have saved hours- lessons learned. I am working on the x axis next but I will be busy with the day job for the next week...

Thanks for looking

[hesham morsy]

[mcphill]

Hoping for an update, get any work done over the weekend?

[gt40]

Hoping for an update, get any work done over the weekend?

I have been busy and not able to work on things - hope to do more by the weekend.

[serpvect]

Any progress?

[gt40]

Any progress?

Sorry for the lack of posts. We had a change and I am moving up to Seattle area and am getting a larger shop to boot. All busy though getting the house ready for sale so it will be a few months. Basically the base is done and I bolted the linear rails to it.

I hope to restart mid-summer...

[wizard]

I am only 4 years into cnc and it is at the serious hobby stage. I want to make some 3d stuff in limited quantities in steel and I want it to be more accurate than my RF45 clone- these things are the basis for doing this build. In a perfect world, I would have Brother Speedio but as the wife won't sign off on that just yet, this is the current upgrade.

I'm not sure this machine will get you there. I think you are missing some important points. The number one point is that mass isn't everything. The first consideration is that you need securely mounted rails and frankly I'd be worried about the machine tearing out your rail mounting plates.

As far as the design, I am trying to keep each major components at 700 lbs / 300 kg. It will also be bolted on a much larger subframe that will add considerably to the mass I expect the full mill with the subframe( still finalizing the design) will be around 2500 lbs/1130 kg. I got all my rails, thk and nsk 32mm ballscrews and basic materials for 2k so far. Add my time and spindle + electronics pneumatic draw bar and I hope to be well under 10k. I think if I can achieve this price point with the components I am using it should be a major step up from my current mill and hard to beat in terms of cutting ability, accuracy compared other mills in this price.

I am still tweaking the vertical column. 11x12x36 is the current dimensions and re enforced with large steel tube cast inside. Should be about 480lb with the steel inside. This is alot better than the 100Lb or so weight of the RF45 column but it could be bigger.

why not place the square column on the onside and machine it to mount the linear rails.

Most important, when I finish, I will know the machine inside and out and be able to maintain and fix it if need be. Modern VMC's can be very complex and expensive to fix and there is the learning curve. I also would rather start with new stuff than learning fix someone elses mess.

To your comparison with an RF45, I am not sure how familiar you are with these machines. The column is 7x9 tapered hollow cast Iron, as is the base. I can pick up and move the column, the base or the table by myself. The whole machine is only around 800 lbs/350 kg without the motor and stand. Going from a RF45 to this build will allow me to replace dovetails with THK linear rails, 3 times the mass and the room to fit proper sized ballscrews and servos.

Again mass isn't everything. To function better the machine needs to be structurally stronger. In this regard I'm not getting good vibes about this machine.

I am still tweaking the vertical column. 11x12x36 is the current dimensions and re-enforced with large steel tube cast inside. Should be about 480lb with the steel inside. This is alot better than the 100Lb or so weight of the RF45 column but it could be bigger.

You brought up an interesting point on the steel rails. I tested a 1/2"thick piece a foot long cast at the bottom of a box mold placed on a granite surface table. It was dimensionally unchanged. The ground steel will be through bolted to the mold and cast in a horizontal position with the epoxy granite on top in the same manner as my test. We will see for the bigger piece. I guess I will scrape or grout as needed.

For my part, the biggest thing I am trying to work out is mixing 3 - 4 cubic feet of epoxy granite per pour for each section. I have planned for a total of 25 gallons.

Thanks for the challenging questions!

Get a cement mixer!