Sunday, February 18, 2024

Door Locks and Epoxy

Epoxy doesn't mix with locks.

I started the first epoxy pour on the front panel, but wasn't happy with how it turned out. The weight was higher than planned.

The fabric overlapped the edges so I could trim it later. Pulling on this, I was able to peel the epoxy impregnated fabric off.

It only pulled a small amount of foam off. Checking the weight, I was right. The epoxy impregnated fabric weighed 535g. So I was right with 100g fabric and about 440g epoxy.  Way too much epoxy.

The 1200x960mm (1.152m²) piece of foam with some epoxy still on it is 1200g. I weighed some spare pieces and 1m² of foam weighs 1.027kg. This is heavier than the 900g I was calculating on, so the panel should weigh 1184g. There is a little epoxy in the join and on the edges where the fabric wasn't.

Need to do more epoxy testing. I'm reluctant though. Thinking to change to using glue and paint only. Thinking about it. I started some test pieces. It's much easier to use. Still deciding how I'll go forward with that. I'll get the foam pieces squared off first, then coat them. This will give me more time to decide.

I cleaned up the chassis, support legs and drawbar removing rough edges. These were on the inside of the tubes.  I used rags to clean out any aluminium filings.  Also marked up the support legs to cut the adjustment slot. Need to wait for a teacher on that. They'll show me how to safely use the lathe or milling machine.

The door locks I had ordered ended up being a "captured key" type. These are for mailboxes, or cupboards where you put the key in, open the lock, but can't remove the key until you close and lock it again. Easy, I'll just drill a hole in the right place to let the key out. It worked!

Until I taped the lock. Small brass pins fell out. Locks aren't meant to do that: drop their innards out.  The lock jammed up.  As I had two locks, I decided to try drilling between the pins. But that didn't work either. Pins still fell out. Two locks stuffed. 

Saturday, February 10, 2024

First Epoxy Pour! Is it the last?

Doesn't look much, but it's the first panel to be laminated on one side with fabric and epoxy. I've been thinking and mildly stressing about it for a while. 

I was nervous mixing and applying. Worrying about the ratios and measuring them accurately. The "clock is ticking until it goes off" from the start of mixing makes it feel like it's a rush. Don't delay. But measure and mix well. I mixed two batches. I didn't want too long a gap between the batches in case the first poured onto the fabric started setting before I could finish.

It's easier to coat the foam, place the fabric over and then add more epoxy to the top. I did this at first, but once I had started, I  didn't have enough hands to keep the clean fabric off the coated fabric. So I lay all the fabric down and poured the epoxy on top. Much harder to get even coverage. I was getting dry spots. I could force the epoxy through from the top, but it's more time and work. The clock is still ticking. I used a plastic scraper to move the epoxy about and push it through the fabric. Used it like a squeegee to spread the resin out as far as possible.

Start to finish took an hour and used about 440ml of epoxy for about 1m². 

The epoxy is mixed by volume. Very inconvenient. I wanted to calculate by weight as using a scale is easier than eyeballing clear liquid into measuring containers. 

I got a packet of 250ml and 350ml(?) paper cups. Wooden knives held by the blade with the round end of the handle cut off square (to get into the corners) were used as stirrers and scrapers.  I used water and a scale before hand to mark 20ml increments on the out side of a 250ml paper cup. Then transferred the measurements to the rest with a ruler. 

With a light positioned above the cup, you can see the liquid level as a shadow on the outside to mark it read measurements. 

I poured 80ml into a cup, weighed that, then poured it into the larger cup, scraping out as much as I could with a knife scraper. 3g remained in the cup. Poured another 80ml and emptied it into the large cup. 3ml remained behind. That's 2x part A. Using a new cup and knife scraper, measured 80ml of part B and poured it into the large cup. Again 3ml remained behind. 

By the weights, that would be 87+87=174g Part A with 77g Part B. Total weight 251g

(For the second batch I used only the large cup and measured 90+90=180g part A, 80g part B. Total weight 260g.)

On pouring part B into A, I started a timer and using a new knife stirrer, started stirring for two minutes. Then scrapped the edges and bottom and mixed for another two minutes. Called it ready. That's 4 or 5 minutes of the 30 minute working time gone.

Total weight of the two batches: 511g. Not all was used on the fabric, but at least 400g was. 

That is way more than I thought it would be. 100gsm fabric, I was working on about the same weight or maybe double, of epoxy. Did I apply it too thick or did the fabric soak up when I was forcing it through? The fabric is 80% polyester and 20% cotton. 

I'll have to think about this. Besides the increased weight, I'll need a lot more epoxy. The epoxy was originally purchased to use as a glue for the foam, and as a bonus, in the smallest volume I got, seemed enough to coat the panels as well. I didn't end up using it for gluing, as a one part polyurethane glue was easier to use. 

Not sure the epoxy it's worth it. I will still need to paint the epoxy to protect it from UV. It might be better to simplify and skip the epoxy and just use paint and the fabric: also known as "Poor Man's Fibreglass".