[the_canuck]

Yes, I'm trying to get flat surfaces to mount the linear rails on. The steel is not level inside to outside and one side is bowed a bit in the middle.

Epoxy should self level with gravity giving me a very flat surface.

Fingers crossed.
Andrew

[amishx64]

Very interesting. The reason I'm asking all these questions is because I am going to build a steel construction machine approximately the same size as what you have. I'm in the design stage and have gathered some parts.

I was hoping that I could just get away with bolting the rails to the cold-rolled steel...

At any rate, I hope the epoxy method works. Good luck!

[PaulRowntree]

Which epoxy are you using here? How much of a bow in the metal would it be reasonable to flatten out this way (ie is it possible to have too thick an epoxy layer?).
Cheers!

[the_canuck]

The dams are holding. I had a couple minor leaks.

I lowered the wire a smidge to minimize the thickness of the epoxy needed. It will be about 3mm thick at the center of the rail once cured.

I'm using West Systems 105 with 206 Slow Hardener. I used 300 grams for a single bed. I should have added a bit of acetone to lower the viscosity. I'll try that on the second bed.

One tip, you don't have much time so make sure everything is set and ready. Even with the slow hardener you only got about 20 min. before it starts to thicken. Even less if you are trying to self level.

207 hardener is probably a better choice for this but I didn't have any on hand.

I used a heat gun to pop bubbles once the epoxy was down before it started to flash. This works like a charm. It's a trick I picked up while making epoxy molds for model airplanes.

Now the long wait begins. It takes about 24 hrs to set and a week or so to fully cure. Time to find a granite parallel or straight edge so I can lap the epoxy once cured.

This rail is the most out of flat of the two. It's off about 1mm from flat on the inside to outside and down in the middle of the long axis by about 5 thousands or so. The other side doesn't have the long axis bow but it does have the short axis issue. The 2x6 came as a parallelogram instead of a rectangle. 1mm is bad but not when you think about how the steel gets to be a rectangle.

Andrew

[CarveOne]

In reading about epoxies in general, I found that thinning it with acetone actually weakens the epoxy and makes it take longer to cure. I know this is true for West Systems 105 with 206 Slow Hardener as I use it at home and for my past UAV/RPV work, though it cleans brushes and other tools well.

The ambient temperature of the room you are working in has a lot to do with how fast it starts to set up. Doing this early in the morning when it's cooler, or turning the air conditioner (if you have one where the machine is located) on "blizzard" setting will work better than adding acetone. We get 1+ hour working times on large lay-ups if the room stays fairly cold.

If you want a very hard surface, get some Cab-O-Sil from Aircraft Spruce and mix some in the epoxy before pouring it. Use enough that the epoxy becomes milky looking but is still drippy.

CarveOne

[cornbinder23]

Cab-O-Sil is a trade name for colloidal silica, It can be had at boat building supply houses as well, which is where I purchase mine.
I use it mainly for filleting work on wooden boats.
I would definitely recommend using respiratory protection when ever you are mixing "Cab-O-Sil" as the affects from inhalation are permanent
Here is a pic of what a particle of colloidal silica looks like
Nasty stuff to be breathing
But that is great advice Carve, for a very stable and hard surface.
Sorry for the useless trivia, your build is looking good Canuck!
looking forward to seeing more progress.
What part of Canada are you located?

JTCUSTOMS

[ger21]

If you pour the epoxy into a large pan after mixing it, you'll have much more working time.
The large mass in the cup causes it to get hot and start curing very rapidly. When spread out in a pan, it will stay cool and you'll get much more time.

[the_canuck]

I'm very familiar with colloidal silica. I have some in my shop along with about every other west system additive they sell. It's nasty stuff on the lungs as is a lot of stuff we 'play' with in the model airplane building relm.

For this application, the longer working time you have the better as it gives gravity more time to work it's magic. Thinner viscosity also is a big help thus adding fillers is not what I want to do. West is actually not that thin so it isn't the best choice for this application but it's what I have in the shop. In the past I've used thinner epoxy's for laminating and they would be a better choice for self leveling.

I'm not too worried about strength as it is just a thin flat surface to mount the rails on. It will be approx 3mm thick at the thickest point under the rail.

Pot life wasn't my issue. I mixed the parts together for about 2 mins and then immediately poured it into my dam. By the time I had it evenly distributed and the larger bubbles dealt with it was already starting to thicken. Once thick it will no longer self level so you need to be careful not to mess up the surface.

Andrew

[the_canuck]

I'm located in Denver Colorado. I grew up on PEI.

Andrew

[Zygoat]

denver? i live in fort collins, but most of my family is in the denver area. we might have to get together some time. talk about cnc, computers, rc planes and other nerdy stuff. :rainfro:

[the_canuck]

Any one is welcome to stop by the shop in the evenings or weekends. Just call ahead.

Epoxy didn't turn out as I wanted. It didn't self level as good as I hoped. I am thinking I have a lot of sanding in my near future.

Andrew

[CaptainVee]

epoxy is a pain to sand but it goes soft at 70 degrees c. That may be worth trying.

[amishx64]

Epoxy didn't turn out as I wanted. It didn't self level as good as I hoped. I am thinking I have a lot of sanding in my near future.

Sorry to hear that. Do you think it was the drying process or was it uneven from the pour?

[cornbinder23]

MAS makes a low viscosity resin that I have used for very similar applications and it works great at temps above 60F, it self levels great and de-gasses fast
The best part about MAS stuff IMO is the fact it has no odor or voc's:cheers:

JTCUSTOMS

[mikemacwillie]

How about a low viscosity urethane resin? It's very hard when cured, and it will self level due to its low viscosity. Smooth-Cast® 320, 321, 322 Product Information | Smooth-On

[the_canuck]

Urethane would cure too soft to make a good bed surface I did send an email off to precision epoxy to see what they recommend.

Andrew

[vikingboy]

I just read thr specs on the Smooth on stuff and the ONYX type has a hardness of 80 and a compression strength of over 8000 psi hardly soft.

Andrew

[vikingboy]

Some of the smooth cast stuff is very hard the Onyz type for example has a hardness of 80 and compression strength of over 8000 PSI, not too bad, the 380 and 385 type with fillers are also made specifically for industrial use and seem interesting also.

Andrew


Sorry for double post, confussion when editing.

[the_canuck]

I have some of that stuff in the shop which I used for another experiment. 80 hardness I think. Still not as stiff as epoxy.

Andrew

[the_canuck]

Good News!

I was able to salvage my pour. I decided to at least try and sand it flat. I started with my belt sander and 120 grit to knock down the basically flat as the edges were higher than the middle. Next 60 grit with a 36" block made from a 2 x 3 steel piece that will be used for the gantry. It was fairly flat. That got everything even across the length. Next more 60 grit on a Grade A 12" granite parallel. After 10 mins or so on each pass I layed down a layer of dykem and kept checking along with the machinist level. Once I thought I was really close, I started with 320 Grit on the granite parallel. Checking with my 48" straight edge and a feeler gauge of 1.5 mil I'm getting about 98% flatness with only one small spot on one end of the bed less than 2 inches from the end. The machinist level is showing I'm withing 0.001 of level checked every 6 inches or so.

Whole process took approx. 3 hrs of sanding work!

I'm happy! Now to repeat the whole process for the other rail.



I'm satisfied!