DIY - ACRYLIC BENDING TABLE - (Update 9-28-13)

[rablack97]

I figured everyone in here has thought about or wanted to bend some acrylic, so i figured I'd attempt to document a build on one for the forum.

This isn't an original idea as there are tutorials out there on how to build these things, just figured it would interest a few folks that may want to build there own as well.  It's also an alternative to the dreaded heat gun weight it down with clamps theory .

I'll be asking electrical questions as i suck as electrical formulations, amp, watts, voltage etc...

The idea is to make it as safe as possible, fairly efficient, durable and cheap to build, hopefully under $100.00

• The area will will be about 36X40, i doubt i'll be bending any CP panels wider than that.
• It will have an angle set/stop
• On/off switch
• Variable heat control
• Portable

Here are some of the parts I'll be looking into, and testing during this process.

• 12v 5a power supply, 24v 10a power supply
• Nichrome wire
• 12v dimmer
• Led voltmeter
• Angle finder

I'm trying to keep the output DC if possible AC scares me.

I'm in the process of ordering parts now, and will post photos of the build, I'm also researching nichrome wire and its heating specs (hence 2 types of power supplys).  12v should be plenty for a CP overlay, but thicker plexi may call for higher voltage/heat.....

Anywho, any comments or suggestions are welcome, especially on the electrical side..Looking forward to the project...

[SavannahLion]

Look at brakes. I have angle iron from an old bed frame i've been meaning to slice up for this purpose.

[PL1]

I'm guessing you already know the trick about using a spring to take up the slack/sag created as the Nichrome wire expands/lengthens due to heat, right?

It would be great to incorporate swappable bend radius forms (green) so you can choose between several bend diameters.

The heater (red) is mounted on an adjustable-height support frame that allows you to heat the bend point.

An adjustable roller (blue) keeps the plexi close as you bend it to the desired angle.


Scott

[PL1]

Forgot to mention earlier, but IMHO that style of angle finder sucks big hairy green .

At best, the scales are hard to read accurately and at worst it may even be a Communist plot to make users victims question their competency and even their sanity. 

A simpler design like this is easier to read and far more accurate.   




Scott

[rablack97]

Thanks guys, for the input.....noted

Forgot to mention earlier, but IMHO that style of angle finder sucks big hairy green .

At best, the scales are hard to read accurately and at worst it may even be a Communist plot to make users victims question their competency and even their sanity. 

A simpler design like this is easier to read and far more accurate.   




Scott

Lol Scott,

I know they suck.....buttttt lookie....

Its got mounting holes, a brass lock, and the longer part stays stationary allowing you to select angle, shorter part it the actual stop the bending board can rest on.....

I agree on accuracy as well, give me some ideas on how to mount that thing, and i'll look into it.

I'm guessing you already know the trick about using a spring to take up the slack/sag created as the Nichrome wire expands/lengthens due to heat, right?

Yep, will be using tension springs to take up the slack.


Never thought of having this thing bend down, but wouldn't that limit the rig to be used at the ends of tables only.

For the the radii swapout, what about different thicknesses of dowel rods?



I was thinking about the compress roller as well, as i'm trying to keep things low cost, what about small quick release clamps.  I'm not sure how to get compression on the roller or or pull it down and have it stay.

Something like this could work too....



My question to you is on the electrical, I'm not sure what to use for the power in regards to amperage and watts.....

Per here plexi is pliable at 275F degrees.  I know this varies based on thickness.

http://www.sdplastics.com/polycast.html

Since I'm using 20awg Nichrome wire....these are the specs to get this wire up to a good heating temp.



So a 6amp psu should get me well over what i would need for thicker plexi if need be.  I'm just not sure if its the watts or the volts that i need to look at when it comes to heating.

5 amps at 10V AC if 50 watts right, what would be the DC equivalent of that?

[welash]

The voltage will depend on the length of the wire.  The temperature is going to be proportional to the current (amps).  The current is going to obey ohm's law E=IR, where E is the voltage, R is the resistance, and I is the current.  You need to know the resistance of the wire per foot, and the length to get the total resistance.  I looked up a value for 20 AWG nichrome wire as about .66 ohms per foot.  If your wire is a foot long, that would be 6amps * .66 ohms or about 4 volts.  There is a nice web based calculator at http://www.jacobs-online.biz/nichrome/NichromeCalc.html that seems to agree with that (honestly, that is where I got the value for the resistance per foot).

The power in watts will be the voltage multiplied by the current.

[opt2not]

I fully endorse this project!  I've always thought about a dedicated table/tool for bending plastics...this looks promising!

[rablack97]

The voltage will depend on the length of the wire.  The temperature is going to be proportional to the current (amps).  The current is going to obey ohm's law E=IR, where E is the voltage, R is the resistance, and I is the current.  You need to know the resistance of the wire per foot, and the length to get the total resistance.  I looked up a value for 20 AWG nichrome wire as about .66 ohms per foot.  If your wire is a foot long, that would be 6amps * .66 ohms or about 4 volts.  There is a nice web based calculator at http://www.jacobs-online.biz/nichrome/NichromeCalc.html that seems to agree with that (honestly, that is where I got the value for the resistance per foot).

The power in watts will be the voltage multiplied by the current.

awesome, thanks for the link and the knowledge, i figured this would engage good conversation about electrical....

I fully endorse this project!  I've always thought about a dedicated table/tool for bending plastics...this looks promising!

I hope folks find it useful and entertaining as well, it will be on the fly and trial and error.

[PL1]

give me some ideas on how to mount that thing, and i'll look into it.

Whether you end up using an up-bend or down-bend setup, design the table so that the top of the working surface is level with the center pivot point of the table arms.

Put the pivot point of the Protractor at the pivot point of the table arms.

The rest of these directions are for a down-bend table (fixed arm on the left, movable arm on the right), but can be easily adapted for an up-bend table.

Two screws through the protractor arm into the movable table arm.

On the back of the protractor face, attach two L-brackets on the part by the fixed arms using epoxy, spot-welding, or small countersunk screws sunk flush or slightly below flush.

The L-brackets allow you to fine-tune the angle by using screws that come up through the fixed arm and several nuts layered like this:

Upper adjustment nut
L-Bracket
Lower adjustment nut
 (small gap)
Nut to hold screw firmly to fixed arm
Split or star washer
Fixed arm
Screw head under the fixed arm

Never thought of having this thing bend down, but wouldn't that limit the rig to be used at the ends of tables only.

True.

The top-heat down-bend design uses gravity to assist the bend.

A bottom-heat up-bend design traps rising heat better.

Either concept works as long as you remember to heat the outside of the curve.

I also have a dual-heater (top/bottom) up-bend design with a hinged upper heater that swings out of the way of a lockable hinged bend form -- this design is for working with thicker plexi.  LMK if you are interested.

For the the radii swapout, what about different thicknesses of dowel rods?

Dowel rods won't work very well because they are different diameters which changes the bend point.

Use a router and several roundover bits to shape 1x2's into swappable forms secured by machine screws and t-nuts.

I was thinking about the compress roller as well, as i'm trying to keep things low cost, what about small quick release clamps.  I'm not sure how to get compression on the roller or or pull it down and have it stay.

Something like this could work too....

Either that or two of the el-cheapo Harbor Freight bar clamps connected to a slick flat-bottom "sled" sounds good.

Before clamping down, put a piece of thick paper or thin cardboard between the plexi and sled.

After clamping down, pull out the spacer and you have just a bit of wiggle room.

Alternate method -- use some sheepskin wrapped around the clamp bar and press down gently as you clamp.

My question to you is on the electrical, I'm not sure what to use for the power in regards to amperage and watts.....

On this, I'll defer to the interactive calculator that Welash linked.


Scott

[PL1]

Several thoughts to consider about the channel that the heating element sits in:

How do you plan to insulate the wood body from the heating element?

Most builds use aluminum U-channel. 

What about ceramic tile? (heat resistant, non-conductive)

With these temperatures, how much more formaldahyde will the surrounding MDF off-gas?


Scott

[rablack97]

You've given me alot to think about Scott,  , great ideas though....

I'm going with a bend/up design currently.

I was going with an aluminum u channel, I've seen melamine, mdf, and osb board used.

I read about creamic tile as well, some have mentioned ceramic spaces too.

Then theres also fiberglass tape.

Several thoughts to consider about the channel that the heating element sits in:


With these temperatures, how much more formaldahyde will the surrounding MDF off-gas?


Scott

Lost me there.

[PL1]

With these temperatures, how much more formaldahyde will the surrounding MDF off-gas?

Lost me there.

The adhesive holding MDF together is made with formaldahyde.

This is why you need to use proper respiratory protection when cutting/routing it so you don't breathe in those fine particles and absorb the carcinogenic (cancer-causing) formaldahyde.

MDF releases (off-gasses) formaldahyde for several months after manufacture and also when you cut the MDF exposing a part that hasn't off-gassed/cured yet.

Picture a thick slab of concrete where the surface looks dry, but it takes a long time to fully cure -- Hoover Dam was built in 1931-1936, but the concrete is still curing today.   

At higher temperatures, MDF releases more formaldahyde than at room temperature. (greater heat = faster molecular movement --> more gas released)


Scott

[rablack97]

Was actually thinking about laminating the mdf, would that help or alleviate some these issues?

[PL1]

Was actually thinking about laminating the mdf, would that help or alleviate some these issues?

Anything that seals the surfaces such as painting will prevent off-gassing.

Not sure if the laminate you're using is gas-permeable or not -- seems like it would have to be for the adhesive to cure. 

Probably wouldn't hurt to prime it, scuff it up for better adhesion, and then laminate.


Scott

[DaOld Man]

I may be missing something here (I usually do), but that dimmer you pictured is only good for .8 amp (800 MA), looks like the lowest rating in that chart is 3.8 amp (3800 MA).

I like your idea and will be watching.

[rablack97]

I may be missing something here (I usually do), but that dimmer you pictured is only good for .8 amp (800 MA), looks like the lowest rating in that chart is 3.8 amp (3800 MA).

I like your idea and will be watching.

Every where I've looked at the description for this thing it says 8 amps. As this is a strip lighting dimmer, most strip lighting starts off at about 2 to 3amps, so .8 wouldn't even operate the strip.....

However you maybe right in a sense the way its labeled, these are the specs.

Specifications:

Working temperature: -20°C ~ 60°C

Supply voltage: DC 12V

Output power: < 96W

Output current: < 8A

Output: 1 channel

Static power consumption: <0.5W

Size: L89×W59×H35mm

Was actually thinking about laminating the mdf, would that help or alleviate some these issues?

Anything that seals the surfaces such as painting will prevent off-gassing.

Not sure if the laminate you're using is gas-permeable or not -- seems like it would have to be for the adhesive to cure. 

Probably wouldn't hurt to prime it, scuff it up for better adhesion, and then laminate.


Scott

I'm wondering if you would even get the reaction your talking about, given the heat is only applied for a few mins and would be controlled.

As far as adhesion, i've been laminated alot lately on mdf and adhesion is good, unless your recommending the priming more as a sealer.




Here are some other options, I've been looking into for power.  The dreaded AC options.

The cheapest way I've found so far is using variable speed controllers, or a household wall rotary dimmer switch.  This is the alternative to buying and expensive variac transformer.

This guy is 14.99 with 25% off coupon from harbor freight.....



Only thing is I'm not sure what the ramp up or start voltage DC this thing would kick out as its used to power tool.  However the idea would be to take a PC power cord and alligator clip the ends to the nichrome wire and use the controller for power output.

Same theory for this guy...These are about $6.00



This one i think would integrate better with the build as it can be installed into the frame rather than having an external corded controller.

The only issue with AC is that the digital readouts are harder to source that start out at 0.  However a jack for multimeter probes might work too for the voltage readout....

[orion]

I use nichome wire all the time with my electronic cigs. It doesn't take much volts to heat it up that's for sure. If you use it make sure you build the table in a way where the wire is easily replaced, you will burn it up eventually. Consider using kanthanal wire as it holds up a bit more, its way more robust. I hear titanium wire is really nice for a heating element as well.

[PL1]

I'm wondering if you would even get the reaction your talking about, given the heat is only applied for a few mins and would be controlled.

As far as adhesion, i've been laminated alot lately on mdf and adhesion is good, unless your recommending the priming more as a sealer.

The primer is only there to seal the MDF.

The formaldahyde exposure level is probably not going to be very high, but priming the MDF should stop it completely.

The formaldahyde will off-gas at room temperature and exposing it to higher temperatures will speed the process.

Picture how long it takes to boil water -- only a few minutes of heat and the gasses in the water are bubbling away.

If you don't prime the whole thing, at least prime any MDF that is within ~4 inches of the heating element.


Scott

[rablack97]

Not dead guys just been working through the build.

I'll have more photos.....

The table will be a 4X4 with a 36" width bending capability.  Not gonna worry too much about multiple radius templates, just looking for a nice clean bend w/o ruining the acrylic....

Decided to go with Particle board, a 4X8 sheet $18.00, whole project was done off one sheet.



I wont bore you with basic wood working 101 table top stuff...so all i did was butt-up 4 2x4's in to a 4x4 square and secured the particle board to it.

Base is done, thinking of keeping it low profile for easy storage, instead of adding legs.



Also these came in, one is 3A the other is 6A, i'll be testing both as soon as the nichrome wire comes in.



I'm further than it looks, just wanted to let folks know i'm working on it....

 


 

[DaOld Man]

Keep up the good work.

[PL1]

Looking good so far.

What are you using for hinges?

Have you designed a mechanism to hold the bend at a preset angle until it cools?
(Consider using perforated angle iron, a crossbar, and two turnbuckles -- one for the left side, one for the right.)

Given the width of the bend table, consider having a protractor on both sides to verify the bend is even.


Scott

[rablack97]

Looking good so far.

What are you using for hinges?

Have you designed a mechanism to hold the bend at a preset angle until it cools?
(Consider using , a crossbar, and two turnbuckles -- one for the left side, one for the right.)

Given the width of the bend table, consider having a protractor on both sides to verify the bend is even.


Scott

Just using some simple strap hinges.  Works pretty good.



Holding Mechanism, still haven't figure that one out yet....I need this, but have no idea what that is or what it's called (Yellow miter guage looking thing.

That would kill 2 birds with one stone, possiblly, the weight of the bending board is kinda heavy.



I'm having a hard time tryin to figure out strong angles stops for the bending board, to your point for set cooling time.

[PL1]

How about this?

Perforated angle iron (yellow) is bolted to the sides of the fixed part of the table, flat side down.

A plain metal rod (red) about the same size as the holes in the angle iron serves as a crossbar for rough angle adjustments.

On the underside of the folding part of the table there are pivot points (green) that connect to turnbuckles (blue) used for fine angle adjustment.

The other end of the turnbuckle has a bolt through the second hole of the horizontal side in another piece of angle iron (gray) that is flat side up and vertical side out.

Use an eyelet or heavy wire through the first hole in the angle iron to secure the turnbuckle end from pivoting on the angle iron.

The threaded crossbar (orange) between the turnbuckle arms holds them a fixed distance apart.

As you lift the folding part of the table, the turnbuckle arms slide across the adjustable crossbar until they drop into place.

If you use the same size turnbuckles, you can even make two swappable sets of turnbuckle arms -- a long set for high angles, a short set for low angles.


Scott
EDIT: Added closeup of the turnbuckle arm end with a better design.
Top lip catches the arms as they fall into place, rounded bottom right corner reduces overbend/bendback on the plexi while locking the arm into place.

[rablack97]

I like the idea, although i'm already a 2ft. in length....wouldn't that make it gargantuan?

Also, how would it accommodate angles less than 90 degrees....

[PL1]

Remember that the diagram above is not drawn to scale and is only intended to show how the various pieces described in the text fit together. (I'm not a wizard at renders like Maximus  )

If you only made one 2'10" (long) set of pivot arms, the yellow part would need to extend not more than 4'10" past the bend point.

To provide better support for low angles, you will also want to make a short set of pivot arms.

Rough adjust angle by moving the red crossbar to a closer or farther hole. (see angle adjustment slots in pic below)

If the red crossbar was inserted 4'10" past the bend, the table would be flat and so would the pivot arms.

If the red crossbar was inserted 2' past the bend, the table would be straight up at 90 degrees and the pivot arms would be at 45 degrees.

You can make the arm lengths 50% shorter by moving the pivot points to the middle of the folding part (1 foot from the bend) like this adjustable back chaise lounge -- the down side is that you have less fine angle adjustment and less leverage to support the table.



You can make the yellow arms removable for transport/storage.

You can also remove the pivot arms for transport/storage by turning the turnbuckles until they come undone.


Scott

[rablack97]

Yeah, thats what I thought you were going for, to your point that route limits angle adjustment.

Do you know of any long arm pneumatic door closers...I've seen a few but the arms aren't long enough...

[rablack97]

ok found it.......ouch $40.00

[kahlid74]

Subscribed.  I look forward to your progress!

[PL1]

ok found it.......ouch $40.00

Ouch indeed.

Why not print your own protractors using Cory's serial plate technique.

Several patterns to consider here, here, and here.

Use some plexi with an etched line for the swing arm.


Scott

[rablack97]

Ok small update....

Added the 2nd Layer so the plexi will be even with the bending side.  I was toying with some ideas, hence the layer being in pieces.  However this will be laminated and covered.

Aluminum channel and hinges test installed.



I made sure there was a 1" lip for the bending side, as this will aid in lifting the panel.



The is the guide made from an aluminum strip to keep the acrylic square



Added a handle for pickup and storage



Bending panel at a 90 degree angle, very easy to lift.



For the electrical, i wanted to keep thing as low profile and hidden as possible, mainly for safety.  So i drilled a hole and used an an L-Bracket to support a bolt.  The wire from the PSU will go here via a circular crimp connetor.





From above.....2 nuts will hold the nichrome wire in place, the plasic will be removed from the connector.



A smaller type of this will be installed over the screw so no accidental touches.



For the tension bar, i just used a heavy metal bar and drilled holes as each end.



This will be held in place with wingnuts.



The purpose is to keep the plexi from moving during the bend instead of using your hand to stabilize.



Received some more pieces today, nichrome wire and the voltage dimmer....thats all for now...

[rablack97]

ok found it.......ouch $40.00

Ouch indeed.

Why not print your own protractor overlays using Cory's serial plate technique.

Use some plexi with an etched line for the swing arm.


Scott

Think i'm going digital man, i cant figure out a rig to have accurate stops, so i guess my hand will have to be pretty steady at the hold point.

Ordered one of these today, should be easy to take apart and mount at the front of the bend board and it will read out the angle and you move the panel up and down, read up to 360 degrees.

[PL1]

i cant figure out a rig to have accurate stops, so i guess my hand will have to be pretty steady at the hold point.

Why wouldn't the crossbar and turnbuckle setup I posted earlier work?

You can set the coarse angle with the crossbar and fine adjust the angle using the turnbuckles.

Once you set the correct angle, disengage the pivot arms and return the table to flat.

Install and heat the plexi.

Once the plexi is heated, lift the back until the pivot arms drop into place on the crossbar.

Unless I'm really missing something, this should yield easily set and repeatable angles.


Scott

[rablack97]

i cant figure out a rig to have accurate stops, so i guess my hand will have to be pretty steady at the hold point.

Why wouldn't the crossbar and turnbuckle setup I posted earlier work?

You can set the coarse angle with the crossbar and fine adjust the angle using the turnbuckles.

Once you set the correct angle, disengage the pivot arms and return the table to flat.

Install and heat the plexi.

Once the plexi is heated, lift the back until the pivot arms drop into place on the crossbar.

Unless I'm really missing something, this should yield easily set and repeatable angles.


Scott

Ok i had to relook at your rig, i didnt quite understand it, the adjustable cross bar is what put it all together.

You think it could be rengineered to be w/i the base.....

Cut a hole in the 1st layer and have it pivot in and out of the base?  Trying to keep in sorta compact.

[PL1]

Ok i had to relook at your rig, i didnt quite understand it, the adjustable cross bar is what put it all together.

You think it could be rengineered to be w/i the base.....

Cut a hole in the 1st layer and have it pivot in and out of the base?  Trying to keep in sorta compact.

I think it would be easier to use 2 bolts or threaded knobs like this to hold each yellow piece to the fixed part of the table. (DimcoGray makes  a wide variety of styles/sizes)



It will be large when in use, but when you remove the yellow angle iron and pivot arms, it stores in a very compact space.

You can use similar hardware on the orange crossbar to break down the pivot arms for compact storage / transport.

Please consider making two or three sets of pivot arms.

A long set for sharp bends 45-120 (?) degrees, a medium set for 10-50 (?) degrees, and a short set for 1-15 (?) degrees.

The exact ranges and lengths to use will depend on how everything fits together.

The main thing you want to avoid is overextending the arms at the bottom of the range -- picture trying to hold a heavy weight at arms-length.

Added an arm end design for bends over 90 degrees.


Scott

[PL1]

Found a great deal on 7-1/2" turnbuckles here that should work great for this design.   




Scott

[rablack97]

Well I did some testing on the PSU's and the nichrome wire, and have had no luck....

Seems these PSU's have Short protection, which i assume that they shut down when + & - touch.....

Anybody know away around this?

[404]

Well I did some testing on the PSU's and the nichrome wire, and have had no luck....

Seems these PSU's have Short protection, which i assume that they shut down when + & - touch.....

Anybody know away around this?

you sure you have the ATX-On wire grounded and are getting power to the psu?

If all else fails, gut a soldering iron.

Been thinking about making a small bender myself. I have a midway cabaret cab that i need to bend a custom wrap around marquee for.

[rablack97]

It's not a Computer PSU...It's these guys



I'm getting power, but as soon as i touch + - together the light starts blinking, as its going into short protection mode....

[PL1]

According to the calculator posted earlier in the thread, 35 inches of 20 gauge nichrome wire will have a resistance of 1.92 ohms.

<2 ohms will probably be seen by most power supplies as a short.

Can you use a 72" length for a heating element that doubles back?


Scott

[melvinbates]

Hmm, what are the specs on the PSU you are using?  You are most likely drawing too much power from it.  You may need to get some power resistors to limit the draw or as PL1 stated double up the wire.  It should be fairly easy to gauge what you will need to do to get it to work.  Just remember Volts/Ohms = Current and Current x Voltage = watts.  Keep that in spec with your PSU and you should be fine.