[pippin88]

Glad the info helps. I did a lot of reading and didn't find a clear write up.

I used two bridges. They are flat MDF cut to length to be a light push fit. I used gaffer tape on the sides.
Attachment 260890

I'm not sure what's ideal regarding width etc. You need it a fair bit wider than the meniscus I think. You want it fairly level with the surfaces. You will lose a fair bit of epoxy to the bridges but that's unavoidable.
My bridges were 1300mm long. I haven't had a chance to check the height between the epoxy yet, but it looks good.



One thing I may not have been clear on in my write up above: I've done 4 separate areas (pours) of epoxy on this build. Each was left a week to strengthen before being disturbed (two, the table and Y rails were done simultaneously). Each pour was made up of multiple batches of epoxy mixed and poured in quick succession. You could mix up enough in one lot if you know the quantity needed and have a large enough mixing container (but beware you'll need to work quickly with that much epoxy in a pot)

[turpija]

what flatness of epoxy surface you expect ? and can you (or will you) check it somehow ? i'm very interested in results

[klaas123]

Me too!

[pippin88]

Progress slowed a bit as I was away for a couple of weeks.

I've done the epoxy for the 4th (rotary) axis on the front of the machine.

Major work has been the Z axis, which is largely done.
Fairly happy with how things have gone. The large backplate is bigger than the working area of my mill, so required a fair few setups to do the edges. Fortunately the holes on the face are all just within the area so could be done in one go.

It's loosely assembled below.

[pippin88]

Work has progressed fairly significantly in a number of areas, but I have found a major problem. I finally got around to checking the epoxy for level and it's not good.

I poured 3 separate areas.
1) Two beams 200mm wide, 800mm long (the beams the Y rails mount to, this is the most critical one). The final epoxy thickness is 3-4mm and these seem to have worked fairly well.
2) One beam 150mm wide, 1300mm long (the front rotary axis area). The epoxy thickness varies from ~1.5mm to ~5mm in a fairly linear fashion from one end of the beam to the other. There is a significant depression in the middle (lengthwise) of the beam of about 0.75mm.
3) A grid with members 50mm wide, 1300mm long with cross beams at 1/3 and 2/3 along length (the table area). Again minimum epoxy thickness of ~2mm. Significant depressions / not level across the grid. The grid before pouring would have had areas 1-2mm low / high.
(I also did the gantry but do have a good way to check that)

I mixed carefully and thoroughly based on weight as per the directions.
I suspect that the problems relate to surface tension / a minimum required epoxy thickness. In 2) the area with the thinnest epoxy (~1.5mm) is proud of the depression, where the epoxy is ~3mm thick and I wonder if the epoxy clung to the area rather than flowing.
With each pour I poured the epoxy over a broad area. I used a pocket blow torch to remove bubbles. The epoxy appeared uniform.

Unfortunately I've now got a few litres of not very level cured epoxy.
I've sent an email to West System to see if they can give any advice / shed some more light.

[klaas123]

What was the temperature? The epoxy thickness should be at least a quarter of an inch so 6,25mm.

[pippin88]

In the mid 20s celsius.

Unfortunately I couldn't find any minimum thicknesses anywhere for epoxy. What is that based on / is it for a specific viscosity epoxy?

For the front / rotary axis area I think I'll be able to shim adequately.
For the table area I'm think I might take a skim cut with the router. This will be smaller than the whole table area. I'll then use a straight edge and work by hand to correct the rest.

It's all a bit hard with no single guaranteed reference surface.
I also didn't realise how imprecise my digital level is. Rated to 0.1º, which is approx 2mm/m (Spirit Level Sensitivity & Accuracy | Degrees Minutes Seconds Converter). Should have got that machinist level instead... (but I had wanted to compare angles etc)

[klaas123]

Temp is ok.

The minimal thickness I found on the website of a epoxy company, can't find it right now.

Have you recalibrated your digital level?

[pippin88]

Yep, calibrated with 180º flip. But it's only rated to 0.1º.

[kimosawboy]

I think your thickness was way off, a heavy 1/8" at least, Epoxy is not that expensive!!!!
Unfortunately you have probably taken down all your barriers and dams... Give it a good clean with some solvent , then a quick sand with 80grit, another solvent clean..then you are back to square one.
Everything looks great so far,I'm looking forward to more progress.
G Vavra

[pippin88]

Thanks for the input. I searched extensively before going down the epoxy route but couldn't find any info on suggested thicknesses. I aimed for 3mm thick but didn't get that in some area. Unfortunately at $200 for 4L epoxy is not cheap, and I calculated needing near that volume.

West System got back to me, but either they have no idea in general or they didn't understand my application / problem, because their reply started with "There is no minimum thickness for WEST SYSTEM Epoxy. It will cure in extremely thin applications".

I'll push on with other things at the moment and see what I can come up with.

[whimsical]

West System got back to me, but either they have no idea in general or they didn't understand my application / problem, because their reply started with "There is no minimum thickness for WEST SYSTEM Epoxy. It will cure in extremely thin applications".

West resins are a little thick I would think. To get it to flow out to a level surface you would be better using a very low viscosity resin, check out some of the resins used in resin infusion lamination they are very thin. A long setup time would be a big advantage as you could warm it up a little to get an even thinner consistency.

[Eldon_Joh]

try system three mirror coat. its 120$ a gallon afaik. and i don't understand why you need to pour epoxy on those beams, just where the rails mount to.

[pippin88]

There are four areas that I need flat surfaces:

Large 200mm wide beams for the dual Y rails - these worked out ok. It's much easier to dam a whole beam than part of one, and the meniscus is significant, so needs to be well away from the actual mounting area.
Gantry - seemed to work out, I did fancy dam building so it does only cover the rail area + some space either side
Table area - didn't work. This is a home welded machine, with no flat surface that I could weld on, so things were out by a few mm here and there. I want a flat surface to mount my work surface to.
Front of machine for rotary (4th) axis - need a flat and perpendicular surface for this and tailstock rails etc.

West System 105+209 has a mixed viscosity of 650 cps. I couldn't find another epoxy with a lower viscosity (at least that's available in Australia).
Mirror Coat is quite a similar epoxy, with mixed viscosity of 700 cps. I couldn't find it in Australia.

In Australia we have less range of a lot of things, and pay a large premium.

[klaas123]

Found the email I got from a Dutch company, epoxy thickness minimal 5mm, width 8 to 10mm wider than the rails (so 4-5mm on both sides of the rail).

https://polyestershoppen.nl/epoxy/ep...thars-202.html

[mbronkalla]

You might consider thinning the epoxy ~2% with acetone. This dramatically reduces the viscosity with modest decrease in strength. WEST SYSTEM - Projects - Thinning WEST SYSTEM epoxy

[pippin88]

I've been slowly chipping away at this.

Everything takes a little longer than I expect...

I've now got a working basic machine.
Things I've knocked over:
Linear rails: Drilled, tapped and aligned the linear rails. This took a fair while. For alignment I eventually used the tight wire method, with thin steel wire over some pulleys with weights hanging on the end. I searched for ages for piano wire, but couldn't find anywhere with thin enough stuff. In the end I found that fishing shops have thin stainless wire with rated breaking strain (fishing leader wire) and it worked great. I used 27lb stuff. It's pretty cheap too. I then used a simple circuit with an LED ring and a razor blade on a cart on one of the linear bearings. When the razor contacts the wire, the LED ring lights up. I was able to get it so along the whole length it just skimmed and only just lit up the ring. I think the rails are straight within 0.05mm per metre or so. This was a painstaking process. I had to turn the heads of the bolts down for the gantry, as I'd hand drilled using the rails as a guide, and the rails are not straight when not bolted down.

Ballscrews mounted and aligned.

Homing (and limit) switches.

Wiring / electronics: Managed to kill a G540 driver (just one of the G250 drivers in my G540) due to making an incorrectly wired connector. I've since moved to a Mesanet 7i43 + 7i76 for step generation, and Leadshine DM856 digital drivers. I'm very happy with the combination. They are very quiet at low speeds, with the G540 the machine was loud at low speeds. I'm happily rapiding at 20m/min. I fit the PC and the electronics in an old aluminium mid tower PC case. I've got some buttons on the front: ESTOP, feed start, pause and stop, feed rate increase, decrease, spindle speed increase and decrease.

Table top: Two layers of 18mm MDF, will have a spoilboard on top. Involved using a very long bit to skim the epoxy flat. Then, because the back table support beam is outside of my cutting area, I had to level it to the others. I used an angle grinder and a straight edge, and just kept grinding until it was flat compared to the other beams. Then drilled and tapped mounting holes. Then drilled the mounting holes in the MDF. Then I drilled a grid of holes, on 6cm centres, and milled pockets for tee nuts to sit in. I have 242 tee nuts in the table. They take a while to install - use a screw to pull them in to the MDF, don't use a hammer (I've seen some people recommend using a hammer).

[pippin88]

Did a bit of cutting today.

6mm carbide single flute spiral, 6mm DOC, 24000rpm, 5metres/min (~200ipm) - cut beautifully.

On my old machine I was cutting at 3mm DOC, 2metres/min with poor cut quality.

Next step is definitely dust collection. I'm going to build a floating dust shoe.

[alan_3301]

Nice. That's a pretty heavy cut.
Good looking machine.

[kimosawboy]

Any updates by chance??? final pics? things you were to do differently?
Really nice machine..

G Vavra