Never Use Poly!

[Cathar]

If that were true, then it wouldn't be used for anything. Protective visors would be cracking in front of peoples faces (they have multiple holes in them for fasteners around the edges as an example).
Five out of six tries that cracked tells me the method was bad, how about you?

Don't know about you. I ride motorcycles. Yes, I've had more than a few visors develop cracks around the stress pressure points where they attached to the helmet. The visors that didn't do this were the more expensive molded visors, which is a totally different method to making visors than the bent plastic sheet with holes cut into it.

Be careful with what you're comparing here. Vacuum formed pre-shaped plastics vs machined/cut plastics. In my experience, the machined/cut visors are more fragile and do develop cracks at the pressure points.

Yes, 5 out of 6 tries does imply something wrong with the method, there's no denying that. What I'm saying is that almost no matter what you do, when you machine plastics you can't guarantee 100% that it will not crack at the pressure points. Yes, you can greatly reduce the chance of it happening, but some will still happen.

 

[JFettig]

yep, thats why i DIDN'T want to use them, I was kinda stuck with them at the time...
now off to find a saw to cut my copper up, then take it to the mill to squair it up :sigh:

 

[wymjym]

mg,
If you want to stay with the 'plastic' top concept buy some lexan and machine it. Use poly fittings with teflon tape and recommend the install as per gemini cool. (always wet the hose and barb area prior to fitting, always turn clockwise, always, always, etc.
But alll kidding aside...lexan will not have the isssues that lesser clear acrylics have. As an example I have a sheet that is 48 x 72 that is screwed into an exterior wall with 8 screws (and washers). This thing acts as a small overhang at an entance to our garage walkin door. It has survived several years of rain, freezing, high winds .......! it is always flexing in the breeze and there is no support or cracks.
Lexan rocks.
wj

 

[JFettig]

lexan, polycarbonate.. same thing?
btw, teflon tape isnt good on the barbs, that puts even more stress on them...
i DONT want the plastic tops, it was just my only or make them, and i figured i wouldnt have to make them, but now look at what im stuck with

 

[wymjym]

yes, the same.
the extra stress caused by teflon tape when used with nylon fittings and lexan(polycabonate) is a non issue.
wj

 

[JFettig]

well i would think it is, cince the excess stress when using a liquid sealant is a problem...

 

[gone_fishin]

Good point wymjym. It is used for windows also and roofing ($40,000+ leaky roofs, I don't think so). Teflon tape is the best thing to use. It's all I use and no cracking on this end. Plastics react with oil mg. Did you use some kind of oil for lubricant when tapping or drilling. That's a no no if you did. How about, did you clean your tap and bits with a degreaser prior to use? They come with a thin film of oil fresh from the store.

 

[wymjym]

nylon fittings>threads< will distort or compress before the 'stress' placed on the lexan will cause a failure. the teflon tape will help keep everything sealed.
lexan is not the same beast you are familiar with
just like the difference of fine crystal (beautiful and fragile) and heat resistant clear cookware. look at the crystal in the wrong light and it will break or shatter....drop the cookware and it might break or not.
I'm not here to argue....lexan will handle your needs if you want to go that route...so will copper/alu. your choice.
wj

 

[JFettig]

I didnt make these tops, the place that made the blocks made the tops, i have no idea...
Ill give the teflon tape a try on the one not cracked top, just for the heck of it if i have any...

 

[wymjym]

the tape will not help you if the tops are not lexan...if they are arylic then you shouldn't waste your time.
wj

 

[JFettig]

yep i know, they are poly

 

[Daemonfly]

I wonder if they hand tapped them or just popped them in a machine tapping fixture.

The machines usually go full down to the end, then reverse back up.

Hand tapping, you can do a little, back off, then go further.

We tried the machines to tap 1/2" - 3/4" lexan for safety shields on punch presses at my old job - more ruined plexi on the tapping machines compared to hand tapping.

 

[dxiw]

IMO Poly is just a hassle and a risk. Why take such a risk when you can get a copper or aluminum top for the same price? What does a poly top give you? TO look at some stupid channels that get boring after 5 seconds. I mean I dont want to insult anyone but you gotta be an idiot to buy poly.

 

[DodgeViper]

I think that there are some that think Plexiglas and Polycarbonate are one of the same. Yes both come in clear and look nearly the same, but that’s about all you could draw a comparison with. Those that are not using Poly are bringing problems onto them self’s. Plexiglas will break just looking at the damm stuff.

Most of the blocks that are on the market have the mounting screws that attach the poly tops to close to the finished edge and are countersinking the machine screws into the top. A button head machine screw is what should be used. I have sheets of poly at work 1” think that are used to machine faceplate to yogurt machines. They are drilled, cross-drilled and tapped, o-rings machined into the face and I have never seen a problem.

I just wonder what percentage of so-called poly tops is really polycarbonate? I don’t think poly tops are getting a fair comparison and many are getting a bad rap, either they have been tampered with or Plexiglas had been used.

I built a heat shield for a linen iron made of a steel frame and covered with 1/8 Lexan. I was not careful at drilling and using rivets to attach the Lexan to the metal. This shield has been in place for over ten years and I do not see any spidering of the Lexan. Lexan is tough stuff guys. Make sure this is what you have.

 

[gone_fishin]

Here here, agree with DV.
dxiw, I buy poly, machine it, and use it without any worry whatsoever. I'll be willing to wager a vast amount of people who would use a waterblock also either have a window in the side of their case or leave the side off. It's only natural for most to want to display what they got goin on in there. That being said, there will always be a market for poly topped blocks no matter how much disinformation is spread by the ones who cannot do it right.

 

[The Overclocker]

Jon, it seems a shame to only offer copper or aluminum tops now, as this waterblock was ment to be a commercial design, you must look at what users want, and the majority want to show off what they have, this means they will like to see inside, try different plastics and different machinging/tapping speeds when making the tops - ask people like gone_fishin how he avoids cracks and stuff, i belive you were already offering a copper or aluminum top to being with, so the people who are scared of leaking tops can still sleep at night.

to sum up, a commercal design needs to sell, and to sell it needs to appeal to the buyer, if buyer wants to see the inside, let them, or they will get something else like the gemini or maze3.

 

[Frodo Baggins]

yeah, what's the point f masks block if you can't see inside :O

 

[JFettig]

ok if you want a poly top, go buy it at case-mod.com, I will NEVER make poly tops or sell them.......and they were machine tapped, The reason i didnt go with copper (explained before) was price, it costs like $2 for a poly top, and $15 for a copper top, and at the time i didnt want to give that up or make the tops, now im stuck

 

[gone_fishin]

What do you mean you're stuck? Do you have a bunch with no tops now or what? Machine tapped means nothing if the operator didn't do a good job. When you go up on a machine tap setup, the tap reverses. If it is not done frequently then it will come out bad and if it is done frequently but forced back down jerkingly it will score the already cut threads which will be bad in a score sensitive material. Doing it by hand is a safer way if you are only doing a few. Get some poly and try it out for yourself. I still think it was not real polycarbonate that you got from them also. If you ever worked with polycarbonate then you should be able to tell immediately if you drill a hole in one of them cracked tops of yours. You can feel the difference, poly is more machinable wheras acrylic will melt on you quickly.

 

[JFettig]

ill give that a shot, im stuck with making 5 tops.. 5 COPPER tops, with my dinky machine...