Heat Treatment Oven

[Kram]

One of these should do it

Big Boy | Shop All Big Boy | Toolstation

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www.toolstation.com

Or Upol Dolphin if you are planning to do anything wanting the best finish.
Theres also a Holts 1k filler which is no good for car stuff but would likely suit this - paint will wet it is the issue.

 

[Dr.Al]

The paint should be RAL 7035 light grey for control cabinets

As you might have seen from other posts I've done, I couldn't care less what the "proper" colour is

The stuff I've ordered was described as Slate Grey and is RAL 7031 (which was described as Blue Grey when I googled that code - one of the reviews I read said it was more blue than grey, but that's fine by me). The high temperature stuff is black as there wasn't much choice in high temperature paint.

I've a whole box of slightly (well a year) out of date intumescent sealer here. Been using it up the pub and it seems fine.

View attachment 479353

I might be heading to Gloucester in the next 3 weeks. You're welcome to 2,3,4 tubes. Unless you find yourself up Kent way?

That's very kind of you. What did you use it on in the pub? To be honest, I don't think it'll be on as I'm keen to get on with painting sooner rather than later (I was hoping to do it next weekend). I think the last time I went to Kent was about 20 years ago!

One of these should do it

Big Boy | Shop All Big Boy | Toolstation

Shop Big Boy at Toolstation • Discover our full range today!

www.toolstation.com

Or Upol Dolphin if you are planning to do anything wanting the best finish.
Theres also a Holts 1k filler which is no good for car stuff but would likely suit this - paint will wet it is the issue.

It's hard to get a feel for how far the fillers would go, but the lightweight filler looks plausible (https://www.toolstation.com/big-boy-lightweight-body-filler/p60837). Shame Screwfix don't seem to sell it (our local Screwfix is a lot closer than our local Toolstation). Any guesses (and I do realise they would be just that) whether 600 ml would be enough or whether it'd be better to buy more than one pack? It's starts getting quite pricey once multiple packs (or even the 3.5 litre, £40 monster pack!) come into play (especially when compared to tubes of exterior caulk).

 

[Onoff]

That's very kind of you. What did you use it on in the pub?

Gaps in the ceiling and round the door frames of which there's lots. Then edges where I've fitted new bits of plasterboard. It's the kind of place where anything you do is an improvement!

 

[Dr.Al]

Gaps in the ceiling and round the door frames of which there's lots. Then edges where I've fitted new bits of plasterboard. It's the kind of place where anything you do is an improvement!

That sounds like mostly wood / plaster rather than metal, is that right?

 

[Dr.Al]

Today was another fairly slow day, but I got a few little jobs done. I'd noticed a bit of scarring on the hinge bodies, so I concluded that the slight roughness in the action was down to the moving bodies rubbing on the (relatively) stationery parts. To sort that out, I used a little bargain basement Black & Decker "power file" (narrow belt sander) to chamfer the edges a bit.

In hindsight, it would have been better to do this before fitting the hinges as I couldn't get the power file underneath the (integral) hinge pin on the hinge pieces attached to the body; I gave them a bit of a rub with some 80 grit wet-and-dry but it possibly could have done with a bit more.

I made the decision overnight that I'm going to paint the cabinet before trying to wire it up. To that end I've ordered some metal paint (which will come towards the end of the week hopefully) and I need to make sure the cabinet is ready for painting. The last few minor jobs to do were some extra holes, first for a three-pin DIN socket that I'll use to connect the chamber door interlock:

That hole needed to be 17 mm and I didn't have an appropriate sized drill, so I used a step drill to drill 16 mm and then a deburring tool (something like this but with a 90° blade that cuts on both edges of sheet metal at the same time) to gradually open the hole out until the DIN socket fitted. I could then drill the two 3 mm holes either side for the mounting holes.

On the right-hand side of the cabinet, I used a step drill to drill a 20 mm hole for the grommet for the incoming power cable and another earthing screw attachment point (not visible in this photo):

The last job I could think of for the cabinet was to make the door latch. This was made out of whatever bits I could find that looked about the right size. The rotating bit was made from some 12 mm × 5 mm steel, with a 6 mm hole drilled in each end and then both holes countersunk (from opposite sides) with a 10 mm diameter countersink. The countersink was used to drill a deep hole in the steel, so it's effectively counterbored and countersunk. The M6 countersunk screws used with it had their heads turned down to 10 mm (as I didn't want them to poke out the sides of the 12 mm steel). I also turned a simple knob out of 10 mm round bar (not shown in this photo);

The door part of the latch was just a couple of bits of appropriately sized steel I found. One was drilled and countersunk; the other (the spacer) already had an M10 hole in the middle, which is plenty big enough for the M6 screw to go through.

The moving part of the latch got screwed into the cabinet with a nyloc nut behind the weld nut so I could tighten it and then lock it in place at the point where the latch moved freely. The fixed part of the latch just got tightened directly to the door. This is what it looks like sealed...

... and open:

Fairly simple, but should do the job.

 

[Kram]

It's hard to get a feel for how far the fillers would go, but the lightweight filler looks plausible (https://www.toolstation.com/big-boy-lightweight-body-filler/p60837). Shame Screwfix don't seem to sell it (our local Screwfix is a lot closer than our local Toolstation). Any guesses (and I do realise they would be just that) whether 600 ml would be enough or whether it'd be better to buy more than one pack? It's starts getting quite pricey once multiple packs (or even the 3.5 litre, £40 monster pack!) come into play (especially when compared to tubes of exterior caulk).

I'd suggest a 250ml tub would have spare by the end of this project. It does however have a working time so thats assuming you mix up just the amount you can use in that time.

Amazon will have it or similar with delivery and slightly cheaper. Couldnt find any with tomorrow delivery tho..

https://www.amazon.co.uk/SILVERHOOK-BIG21-Big-Metal-Filler/dp/B00KX64QNI/

The paint should be RAL 7035 light grey for control cabinets

I would like to disagree..

https://www.mig-welding.co.uk/forum/attachments/img_20220416_195533-jpg.342230/

 

[Dr.Al]

I'd suggest a 250ml tub would have spare by the end of this project. It does however have a working time so thats assuming you mix up just the amount you can use in that time.

Amazon will have it or similar with delivery and slightly cheaper. Couldnt find any with tomorrow delivery tho..

https://www.amazon.co.uk/SILVERHOOK-BIG21-Big-Metal-Filler/dp/B00KX64QNI/

I would like to disagree..

https://www.mig-welding.co.uk/forum/attachments/img_20220416_195533-jpg.342230/

Thanks @Kram. I've ordered a pack of that stuff & I'll see how I get on.

 

[Dr.Al]

On the chamber itself, I'd reached a point of Analysis Paralysis with lots of possible options (stemming from various discussions earlier in this thread) and a complete inability to make any decisions (hence spending a lot of time focusing on the control cabinet instead).

Today, despite having a terrible night's sleep last night, I decided I just needed to make a decision on how to construct it and just get on with it. Whether the decision is right remains to be seen, but it's what I'm doing anyway.

I've decided to build the frame in a similar way to the cabinet (with sheet metal in the gaps) and with a ceramic fibre blanket lining. If I had mortared the bricks together, I think I would have felt okay with the idea of just wrapping them in a simple steel frame (just on the edges) but I didn't like the idea of the central bricks being unsupported. That meant I either needed to put cross-braces on (which I may still do) or I needed to have the gaps in the frames filled in. In the latter case I figured a ceramic fibre blanket may help a little.

Ideally, I'd use bigger angle iron for the frame (to account for the thickness of the blanket), but I've got lots of nicely cleaned narrow stuff, so I'm going to use that and we'll see what happens.

Anyway, with the decision made, I could start preparing the frame:

If you look closely at that photo (it's clearer in later ones I think), you'll see there's a bit of a gap where the angle iron pieces meet. That's a result of changing my mind (repeatedly!) about the construction and cutting some of the pieces a bit short (not allowing for the ceramic fibre blanket). The structure will still be plenty strong enough I think and I can always fill in those gaps later if I can be bothered.

I mentioned earlier that I might add a cross-brace. This is roughly what it would look like:

I'll definitely add one of those (out of some wider steel) on the back of the chamber as it'll give me something convenient to attach the thermocouple housings to, but I'm not convinced the top and bottom need it yet. The sides may benefit from something else for reasons I'll get to in due course.

Anyway, I chucked a load of bits of flat bar into the citric acid bath; hopefully if I leave them until next weekend then the mill scale will come off with less effort than was required with the angle iron.

With the frames tacked together and checked for square, I could weld the pieces a bit more rigidly together, just welding along two seams. In this photo you can see that gap I mentioned before:

It didn't take long at all to get the two frames were welded together:

To fill in the holes, I used 0.8 mm steel, of which I have plenty (all rust free as well!) Incidentally, sheet metal is one of the reasons why I ditched working in imperial years ago (tapping drill sizes and American numbered/lettered drill sizes being some of the others). Working in metric, I measure a sheet of steel as 0.8 mm and, if I want to order more, I find a (metric) supplier and order 0.8 mm sheet. Working in imperial, I measure the sheet as 0.031" (or if I've got a fancy fractional-reading caliper, 1/32"). So I order 1/32" steel, right? No, you have to go and look up what size that is in SWG or AWG as that's what imperial sheet sizes are typically sold as. When I worked in imperial I found I was constantly having to look stuff up; when I switched to metric that all stopped and I rarely have to consult any data books any more. I've yet to find a down-side to working purely in metric so I can't imagine I'll ever go back.

I plasma cut the sheet steel to size, but this time (unlike the control cabinet) I allowed only a 5 mm overlap with the angle iron. That made it much easier to do the tack welds as I could comfortably start the weld on the 12 mm-ish area of the angle that wasn't covered and then carefully draw the bead back onto the thinner sheet. The first few tacks done:

All welded.

I cut a bit of ceramic fibre blanket to size and shoved it into one of the frames:

That shows why I said earlier that it probably would have been better to use wider angle iron. Once the bricks are in place pressing down on the blanket, it'll shrink a little and there will be a small overlap of angle iron to bricks, but it'll only be a couple of millimetres I think. Hence the sheet metal is the thing that'll be holding the bricks in place.

I could probably split the ceramic blanket in two (to make it thinner), but I'm going to proceed as-is for now and see what it looks like as the rest of the frame comes together. Back to work tomorrow unfortunately, so there probably won't be a lot of progress until next weekend now.