Author Topic: New Curtains and Windows (Read 14169 times)

awemawson · « **on:** October 23, 2013, 08:46:46 AM »

No - not for the house, but for my Beaver Partsmaster. I got fed up with coolant escaping from the pvc strip curtains on the end of my CNC mill, and looking at the strips it turned out that there was no overlap. So they didn't always fall evenly and let coolant through the gaps and onto the floor.

eBay provided me with a roll of the proper stuff and I set to. Turns out the ones I took off were cut from a single sheet hence no overlap!

awemawson · « **Reply #1 on:** October 23, 2013, 08:51:39 AM »

The difference in light level inside was amazing and it got me looking at the windows to the front. I'm not sure if they had just yellowed with age or if they were originally bronze, but they were all sorts of hues and rather manky. I ordered up some cut to size 4 mm polycarbonate (good old ebay!) which has been hanging about for a week or so awaiting 'the right time'

Well that time came today. I had set the Traub CNC lathe doing a 'soak test' to see if I'd cured an intermittent axis drive fault so had to babysit it, which let me drill and fit the polycarbonate. What a difference

Leblondmakino · « **Reply #2 on:** October 23, 2013, 06:08:02 PM »

Looks great!

Here is my machine during commissioning. Slightly different guards and no curtains..plus the table is shorter..

John

vtsteam · « **Reply #3 on:** October 23, 2013, 07:32:20 PM »

Looks new, Andrew!

dsquire · « **Reply #4 on:** October 23, 2013, 09:33:49 PM »

Andrew

Your curtains are cleaner than my windows. I'm going to have to talk to the Maid about that.

Cheers

Don

awemawson · « **Reply #5 on:** October 24, 2013, 04:10:12 AM »

I know this sounds daft, but:

The sequence of removing / replacing had to be carefully thought out as you have to reach through the door window opening in the 'closed' position to get at the side windows. I went through the sequence, and then thought - check those are tight, and tried to put my hand through the now glazed door

Obviously it was so clear I wasn't conscious of it

The other plonker moment was when I fitted the first window (left side by the tool turret) having peeled off the paper protective layer, and thought - oh heck look at those scratches - little realising that there was another transparent film on the other side on which were the scratches

awemawson · « **Reply #6 on:** June 03, 2019, 11:45:16 AM »

Definite case of Deja-vu here as I find myself once more (after 6 years) replacing the Polycarbonate windows in the Partsmaster CNC Mill.

I've been using it today to rough profile soft jaws for the Beaver TC20 lathe, and decided that enough was enough - time to change them again.

They have suffered stress cracks radiating from where the screws fix them, and no doubt the coolant hasn't helped. I know that polycarbonate if dipped in IPA solvent will crack at the drop of a hat.

So I fired off and order for a further four 'cut to size' bits of 4 mm which should be here in a day or two, but how to avoid the cracks in the future?

I know that things were a bit tight when I originally fitted them, so at the very least I will use larger clearance holes, but should I do more? Perhaps fit 'top hat' shoulder washers so there is no compression on the sheets, or maybe fit rubber washers to the same end ?

. . . suggestions please

seadog · « **Reply #7 on:** June 03, 2019, 12:29:11 PM »

Maybe the problem is one of the hole surface finish. If it's drilled and is rough then there are lots of stress raisers.Isn't acetone used to put a gloss finish back on polycarbonate? Maybe you could contrive to reflow the surface of the holes.

awemawson · « **Reply #8 on:** June 03, 2019, 12:56:02 PM »

Seadog,

Acetone will dissolve Polycarbonate sheet iirc but IPA will shatter it. I've often wondered why rioters haven't discovered this trick - a little perfume spray bottle with suitable solvent - quick spray on a riot shield, then one tap and it shatters

I think I'm going for larger holes (so more play) with nylon shoulder washers whose spigot is either slightly longer than the sheet is thick, or 2 mm longer topped by a 1.5 mm thick rubber washer so that the sheets 'float' but are contained.

vintageandclassicrepairs · « **Reply #9 on:** June 03, 2019, 04:41:48 PM »

Hi Andrew,
My experiences of drilling holes in polycarbonate has never been good

I changed tactics and use a soldering iron to melt the holes in the sheet
the excess "melt" is easily cleaned off when it has cooled
Oversize holes and rubber / nylon washers will surely help too

John

allanchrister · « **Reply #10 on:** June 03, 2019, 09:17:48 PM »

Simple solution. Don’t drill hole and screw, use adhesive sealant for polycarbonate as used in aircraft windshields and canopies. I think Sika make a suitable adhesive. Perfect for flat windows.

awemawson · « **Reply #11 on:** June 04, 2019, 02:42:29 AM »

Allan I did consider that, and also self adhesive window channel but the problem is getting the sheets into place and fixing them while things set. Obviously the enclosure is rather full of machine and access is a bit of an issue.

allanchrister · « **Reply #12 on:** June 04, 2019, 03:52:25 AM »

Understood Andrew. No way of attaching them from the outside then? I have used a Dremel on airplane canopies running a specially ground drill for poly which tends to melt the poly and ‘seals off’ the stress risers, and make the holes about 20-30% larger than the screw thread dia to allow for some movement. Do not tighten the screws too much and you should be OK. Could use a combination to attach them and remove the screws later??? And fill the holes with Sika.

Good Luck!!

allanchrister · « **Reply #13 on:** June 04, 2019, 03:55:27 AM »

BTW Loctite and similar threadlockers can crack poly as well.

RussellT · « **Reply #14 on:** June 04, 2019, 03:59:11 AM »

Rubber sucker handles might help with mounting from the outside.

Russell

PekkaNF · « **Reply #15 on:** June 04, 2019, 05:31:38 AM »

Pretty sure you have considered rubber well nuts?
https://www.hansonrivet.com/threaded-inserts-2/rubber-nut-threaded-inserts/

Or the problem is the hole?

Attaching these is a challenge. Different thermal mass and thermal expansion coefficient makes mounting challenging. Dunno. What do they use in greenhouses and winter garden?

Any welding and grinding nearby? Some plastics break on ozone and UV. Some plastics is UV protected one side only, specially the greenhouse variant.

WeldingRod · « **Reply #16 on:** June 04, 2019, 08:25:26 PM »

Um, is there any chance you are confusing acrylic with polycarb?
Acrylic pretty much requires special plastic drills or it shatters. Polycarb laughs even when your drill sucks it out of the vice. Speaking from experience :-0
I've never seen stress cracks in polycarb! Are you using some really nasty solvents in your coolant?

Sent from my SAMSUNG-SM-G891A using Tapatalk

awemawson · « **Reply #17 on:** June 05, 2019, 02:01:18 AM »

Definitely Polycarbonate, yes it drills beautifully at the time, it's only later that the stress cracks appear.

No doubt that the soluble coolant and the tramp oil have contributed to the problem, though I do remember that when fitted the current Windows having used the original Perspex ones as drilling templates, some holes were a tight fit.

At the time I thought that it wasn't an issue as polycarbonate is tough stuff, now I know better

nrml · « **Reply #18 on:** June 05, 2019, 02:57:52 PM »

Why not ditch the screws altogether and use a suitable version of 3M VHB tape to bond the polycarbonate to the metal panel. If it is good enough to bond windscreens on cars and exterior fascia panels onto skyscrapers, I can't see a machine window being a big problem.

You can pre-apply it to the window panels and peel and paste as you apply it to the metal. Holding it in place till the glue cures will not be an issue.

awemawson · « **Reply #19 on:** June 05, 2019, 04:30:53 PM »

They are going in an enclosure that has been splashing oily coolant around for decades, getting it clean enough for a good bond might be very tricky.

I think I'll stick with screws (no pun intended!) - if it lasts another 6 years as the last lot did it's not too bad!

David Jupp · « **Reply #20 on:** June 06, 2019, 12:19:05 AM »

Maybe try a little silicone grease on assembly to keep the fluids away from the drilled holes.

awemawson · « **Reply #21 on:** June 12, 2019, 05:57:23 AM »

The replacement 4 mm Polycarbonate windows arrived yesterday - I'd ordered them cut to size. So I started removing the old ones. With the windows removed I was able to get at swarf that previously had been inaccessible.

It was apparent that last time some of the holes were marginally too tight a tolerance with the screw thread binding on the polycarbonate - this probably contributed to the cracking.

I used the old windows as a drilling jig to locate the new holes - some were too broken so the new polycarbonate had to be temporarily installed using what holes that I could locate, then drilling through the holes in the frame of the machine located the rest.

The 'plan' was to enlarge the 6 mm holes thus produced, to 10 mm with a step drill, insert a 6 MM i/d 8 mm o/d nylon bush into the 10 mm hole, and tighten the bolts onto the shoulder of the bush allowing just a small bit of 'float' for the window by means of the 8 mm / 10 mm of the bush and hole. The bush projection 'shoulder' is bang on 4 mm and the sheets measure 3.95 mm.

I'd hoped to re-use the original 12 mm bolts but they proved just too short now the bush was there, for the shakeproof nuts plastic insert to engage, so I suspended operations until an order for some 16 mm ones arrived this morning.

All went well, and the bolts were tightened down to 'no play' then backed off a 1/4 turn. So hopefully there are no great stress risers in the windows and they may just last a bit longer

So - old windows - cracks all over the place - chuck them out ? No way ! Trim them down using the circular saw and release the 'good bit' from the middle to add to the pile of 'may come in useful' bits

howsitwork? · « **Reply #22 on:** June 12, 2019, 03:32:33 PM »

Nice work Andrew.

try sealing the holes with silicon maybe as that’s pretty shock brook and , if there’s been coolant on the frame probably”y won’t stick reliably to the frame but will flex and fill gaps.

I had been told coolant makes polycarbonate fragile by many grizzled engineers of my aquaintance. U see silicon to glue roof poly panels in the green house after gales blew out the glass for the third time,
. So far maybe a little cloudy but working well and have dropped a large blob of cement ont9 it from about 8 feet up with no damage so pleased after 8 years.🙂

Ian

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Author Topic: New Curtains and Windows (Read 14169 times)