Any Electrical Control Experts out there? (Long)

[Doug Shepard]

After thinking over my warped idea for bending PVC by filling it with steam http://www.sawmillcreek.org/showthread.php?t=54302, I think I want to take another look at going with a heat blanket. The steam idea would probably work to make it bendable, but controlling that limp piece of spaghetti to get bends where I want them seems like it could be a bit of a chore.
There's a couple of reasons I'd rather not go with the torch or heat gun approaches. I'm pretty leery of the PVC fumes risk plus both approaches seem like they're going to need 2 people to heat both side of a 6" pipe to do it. I have enough trouble squeezing in shop time without complicating it by having to work around the availability of a helper.

I started thinking about the heat blanket method again. One of things I'd like to try in the future is building some musical instruments. So I'd need a method for bending the instrument sides and using a heat blanket is one of the best methods for doing that. The purpose specific PVC bending tools I looked at a week ago are WAY too expensive but I started asking myself why the same type of heat blankets used for bending instrument sides wouldn't work.

So I started out taking a look at the heat blanket setup on
Luthiers Mercantile (http://www.lmii.com/CartTwo/thirdproducts.asp?CategoryName=Bending%2FHeating&NameProdHeader=Side+Bending+Blanket+%26+Timers). Hmmm - pricewise this isn't all that bad, but knowing how these luthier supply places tend to overprice some of their specialty tools I decide to keep looking.

MSC (http://www1.mscdirect.com/CGI/N2DRVSH?PMSECT=0002008605) has quite a large selection of heat blankets and the prices seem very reasonable compared to LMI.

Their catalog page (http://www1.mscdirect.com/CGI/NNPDFF?PMPAGE=4442&PARTPG=N2DRVSH&PMT4NO=0&PMITEM=03158060&PMCTLG=00&PMT4TP=*LTIP</p><p>)states: Heaters should be controlled by either a temperature control or a externally mounted thermostat. Watt densities from 2.5 watts per sq in to 10 watts per sq in have sheath temperatures from 150 degF to 350 degF respectively

So I looked on their site for temperature controls Ouch - even the cheapest are a bit pricey and everything I've seen looks like they're designed to plug into some sort of specialized rack and socket setup.
This stuff is quickly getting beyond my Ken (and my Barbie too).

But I head over to eBay and find this
Omega #6102 Socket Mount Controller (http://www.omega.com/Temperature/pdf/6100_CONTROLLER.pdf)that goes from 0°F to 500°F. The eBay listing isn't clear if the socket that normally comes with is included but it looks like I can order that direct from Omega for $8.

Would this work? Is there something else I'd need. If this will work, I think I could end up with a 6" PVC bending setup for under $100 and have it available for instrument side bending in the future.

[Luciano Burtini]

Looks to me like you will also need a matched thermocouple or RTD, depending upon the type of controller being offered on ePay. The Omega unit is simply a temperature controlled relay. The temp is read from the thermocouple or RTD and the input is used to turn on or off the supply current to the heating element. Pretty basic controller.

[I am assuming - from the info provided - that your heating element does not have a tempertaure feedback transducer installed. If it does, then the controller will have to be matched to the type and range of the transducer.]

Keep in mind that the input on the relay is expecting a response from a given temperature probe. Using the wrong probe will result in erroneous temperature information and the relay will either stay on or off longer than expected. You may be better off purchasing a matched set (controller, base & probe) from Omega.

Otherwise, what can go wrong :rolleyes:

[David G Baker]

Doug,
I have used movie lights to bend 1 inch schedule 40 PVC but don't know how well it will work with larger pipe.
David B

[Ryan Myers]

Doug, have you considered trying a regular electric blanket. It is a shot in the dark. If you wrap it around the pipe several times it may build up enough heat to allow the pipe to bend. Sch 40 pipe does take a fair amount of heat to bend though. These things have been known to start fires when left on and all bunched up, so they do get hot.

I can bend 4" conduit with my bending blanket. Problem is with 6" pipe is your going to need to heat about 30 - 40" heated section to get the pipe to bend without major distortion.

Another thougth - I built a bending box prior to purchasing my bending blankets. I had less than $50 invested versus $300 for a factory made unit. I made it using calrod elements from the single pot countertop burners. You can bend them when they are new and have not yet been heated. A friend of mine bent up a box out of 16 guage sheet metal. Not exactly a UL listed unit :eek: but I am the only one who uses it and I will never sell it to anyone. Now my unit would only bend 2" pipe. But that is all I designed it to do. It has two elements. If you use three or four elements in the right configuration it would probably be suffecient to heat the pipe suffeciently for bending.

[Jim Becker]

I wonder if the cost ($ & time) of the stuff you need to bend that big plastic pipe might end up costing you the difference of just using metal duct and being done with it... ;)

[David Epperson]

I'm not sure I see much difference in the heat gun approach vs any of the orther methods discussed. Temperature is controlable as far as overheating is concerned, and I can picture ducting the heat gun output into a containing shell of sheet metal or cardboard to soak the PVC. Even direct the air around the pipe while it's heating similar to what the steam soak would do,

[John Terefenko]

As I mentioned in your first post about this why not metal pipe??? No ground wire easy to get bends for and the whole nine yards. Remember with bending the PVC you want a longer radius bend. Why not get two 45 degree bends. You need an oversized blanket to use on 6". My vote is for metal all the way. Metal gates no problems with clogs.