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Help with bending some rod consistently for handles.


MarcusHMM

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Well I am new here, but need some help from the guys that know metal work and bending rod.

I am making some weight throws for use in practice for my 16 yr old daughter and other throwers.  Commercial ones cost $350 to over $1200 and her Catholic school only has bought one.

Practice is tough with 3 or 4 people trying to share one implement.  I made her one last year to practice with and she has gotten pretty good.  Throws the 20lb weight 50 feet as of last practice.

I am bending up some mild steel rod to form the weight throw handles.  It is 3/8 rod bent into an equal side triangle and then a reinforcing triangular flat stock piece is welded into one corner to attache the bag and weight for the implement.  The handle takes a great deal of abuse from the weight and hitting the floor.  

I have used a Harbor Freight bar and rod bender to bend the handle up.  My consistency is not good.  (I know yell at me for Harbor Freight).  They are close but I need to make them within an 1/8th or closer.

I have attached a print of the commercial handle and also of the entire weight throw for reference.  I do not like the design of the commercial piece as I have seen more than one break at the intersection of the cross brace tube and the handle rod.  That is why I am using a solid triangular reinforcing piece and welding it into machined recess cut in the rod that captures top and bottom.

My problems:

I machine the slot in the rod prior to bending the rod using a Bridgeport.  I secure the rod in the bender so it does not slide as it's bent. Or turn as the slots need to be in the same plane  I machined  3/8+ half rounds into the dies on the bender to give me some added control and centering.  That may or may not have been a good idea.

How do I determine the geometry so that each bend is consistent and the slot cut is in  the correct position?   I see the rod change length as it compresses on the inside curve and stretches on the outer curve. 

After I bend it to the angle wanted how do I set it so that it does not rebound.  I have tried over bending and let it return but that is hit or miss.  Should I heat it before I bend it so that it is soft and takes the bend I want?  Or should I put it in a jig to hold the correct angle and heat it so that it takes that angle when cooled?

After it is bent I use a press to force the triangle plate into the handle recess and then weld TIG weld it.  I need to get the size and shape of the handles consistent so that the bags and shackle attach properly and the overall length is 16" from top of handle to base of weight.  

Hope some metal working guys can point me in the right direction to get these done before indoor season in December.

Open to any and all suggestions as to how to make these.  Is my approach sound or am I way off base?

Thanks and if this in the wrong forum let me know or the admins can move it.

Marcus

 

handle_spec.jpg

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I have been using some 3/8 round rod from Home Depot just for convenience sake and was not using that much.  I bought some 3' pieces and they were all of the same quality as far as I could tell. 

Cut it to length and machined the slot and it all was about the same.  Originally i heated it with MAP gas torch and bent it on a jig, but could not keep things level and the end product was not pretty.  That is why I went to the Chinese bender from Harbor.

When I get it figured out and do a bunch for others I will make the trip to the local supplier and get some 12' lengths.

Eventually if I make her a top of the line one for competition I will try Chrome Molly tubing to lighten the handle.  The more weight at the business end the faster you can get the weight moving and the further it goes.  1% at 55' is 6 inches and events are won and lost by half an inch.  The big throwers use tungsten in the weights instead of lead.  That is some serious coin when you need 18 lbs of tungsten.  But it makes a much smaller ball and the center of gravity is further out on the implement.  

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Well I am new here, but need some help from the guys that know metal work and bending rod.

I am making some weight throws for use in practice for my 16 yr old daughter and other throwers.  Commercial ones cost $350 to over $1200 and her Catholic school only has bought one.

Practice is tough with 3 or 4 people trying to share one implement.  I made her one last year to practice with and she has gotten pretty good.  Throws the 20lb weight 50 feet as of last practice.

I am bending up some mild steel rod to form the weight throw handles.  It is 3/8 rod bent into an equal side triangle and then a reinforcing triangular flat stock piece is welded into one corner to attache the bag and weight for the implement.  The handle takes a great deal of abuse from the weight and hitting the floor.  

I have used a Harbor Freight bar and rod bender to bend the handle up.  My consistency is not good.  (I know yell at me for Harbor Freight).  They are close but I need to make them within an 1/8th or closer.

I have attached a print of the commercial handle and also of the entire weight throw for reference.  I do not like the design of the commercial piece as I have seen more than one break at the intersection of the cross brace tube and the handle rod.  That is why I am using a solid triangular reinforcing piece and welding it into machined recess cut in the rod that captures top and bottom.

My problems:

I machine the slot in the rod prior to bending the rod using a Bridgeport.  I secure the rod in the bender so it does not slide as it's bent. Or turn as the slots need to be in the same plane  I machined  3/8+ half rounds into the dies on the bender to give me some added control and centering.  That may or may not have been a good idea.

How do I determine the geometry so that each bend is consistent and the slot cut is in  the correct position?   I see the rod change length as it compresses on the inside curve and stretches on the outer curve. 

After I bend it to the angle wanted how do I set it so that it does not rebound.  I have tried over bending and let it return but that is hit or miss.  Should I heat it before I bend it so that it is soft and takes the bend I want?  Or should I put it in a jig to hold the correct angle and heat it so that it takes that angle when cooled?

After it is bent I use a press to force the triangle plate into the handle recess and then weld TIG weld it.  I need to get the size and shape of the handles consistent so that the bags and shackle attach properly and the overall length is 16" from top of handle to base of weight.  

Hope some metal working guys can point me in the right direction to get these done before indoor season in December.

Open to any and all suggestions as to how to make these.  Is my approach sound or am I way off base?

Thanks and if this in the wrong forum let me know or the admins can move it.

Marcus

 

handle_spec.jpg

IMG_20161112_1131166_rewind.jpg

 

Well I am new here, but need some help from the guys that know metal work and bending rod.

I am making some weight throws for use in practice for my 16 yr old daughter and other throwers.  Commercial ones cost $350 to over $1200 and her Catholic school only has bought one.

Practice is tough with 3 or 4 people trying to share one implement.  I made her one last year to practice with and she has gotten pretty good.  Throws the 20lb weight 50 feet as of last practice.

I am bending up some mild steel rod to form the weight throw handles.  It is 3/8 rod bent into an equal side triangle and then a reinforcing triangular flat stock piece is welded into one corner to attache the bag and weight for the implement.  The handle takes a great deal of abuse from the weight and hitting the floor.  

I have used a Harbor Freight bar and rod bender to bend the handle up.  My consistency is not good.  (I know yell at me for Harbor Freight).  They are close but I need to make them within an 1/8th or closer.

I have attached a print of the commercial handle and also of the entire weight throw for reference.  I do not like the design of the commercial piece as I have seen more than one break at the intersection of the cross brace tube and the handle rod.  That is why I am using a solid triangular reinforcing piece and welding it into machined recess cut in the rod that captures top and bottom.

My problems:

I machine the slot in the rod prior to bending the rod using a Bridgeport.  I secure the rod in the bender so it does not slide as it's bent. Or turn as the slots need to be in the same plane  I machined  3/8+ half rounds into the dies on the bender to give me some added control and centering.  That may or may not have been a good idea.

How do I determine the geometry so that each bend is consistent and the slot cut is in  the correct position?   I see the rod change length as it compresses on the inside curve and stretches on the outer curve. 

After I bend it to the angle wanted how do I set it so that it does not rebound.  I have tried over bending and let it return but that is hit or miss.  Should I heat it before I bend it so that it is soft and takes the bend I want?  Or should I put it in a jig to hold the correct angle and heat it so that it takes that angle when cooled?

After it is bent I use a press to force the triangle plate into the handle recess and then weld TIG weld it.  I need to get the size and shape of the handles consistent so that the bags and shackle attach properly and the overall length is 16" from top of handle to base of weight.  

Hope some metal working guys can point me in the right direction to get these done before indoor season in December.

Open to any and all suggestions as to how to make these.  Is my approach sound or am I way off base?

Thanks and if this in the wrong forum let me know or the admins can move it.

Marcus

 

 

IMG_20161112_1131166_rewind.jpg

 

 

Greetings Marcus,

        Sorry tried to edit... You could make a small bending fixture from 1/4 X1 welded to a plate .  Just cut your stock to length and use a oxy ace torch at the bends holding the stock with vice grips against the form..  I would make the start finish point of the round stock at the 1/4 weld radius mark on your scetch.. This would allow you to just tack weld the bar. The finish plate welded in would bond the parts for strength.. I hope this helps.. 

Forge on and make beautiful things 

Jim

 

 

  

 

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This isn't hard. 1, forget making one, just make a quantity. The quality of steel from Home Depot is poor, it's too inconsistent for decent bent work. It also isn't likely to be very durable for what you need. Just buy a 20' stick from the steel supply. The guys in the yard will cut it in half so you can haul it home. don't ask at the counter, they have to charge per cut, the guys in the yard will just do it. Take a hack saw with you in case they won't, you can tie up their loading dock and guilt the snot right out of them by cutting it by hand without a complaint or looking back. 

Anyway, An equilateral triangle with 3/8" radius corners is easy. each leg is 7.125" subtract 1x the radius of the corners. Weld 3 ea. of 3/4" dia round stock pins 6.75" on center in a equilateral triangle. Pick the corner that will receive the shackle. 3/8" from that pin #1, weld another pin "stop".

To operate place a length of rod longer than needed, be frugal and make the excess just a LITTLE longer than the reinforcing bar. ;)

Now the fun part, insert one end of the rod in the gap between the shackle pin (#1) and stop. Slip a piece of steel pipe down the rod (don't make me tell you a cheater pipe should be pretty long okay?) Using the LET (Leverage Enhancement Tool) (cheater pipe :rolleyes:) with it placed close to pin 2, Pull it smartly to pin #3, allow the LET to slid further out the rod and again pull it smartly past Pin #1. 

Good A-36 steel from the yard shouldn't have much rebound and if you have a long enough piece left vise grips or dropping a bolt in a drilled hole will secure it till you can warm the corners up with with a torch, even a Bernzomatic soldering torch will let it relax and stay.

If you don't have 3/4" rd.  for the pins maybe you can find bolts and drill the holes in the base plate. I assume because the part is welded you have access to a welder. Welding the pins through a hole fro the back side will prevent weld beads interfering with the corners.

NO FOOLING the commercial handles break THERE! Good grief that cross brace is a pair of stress risers right where they shouldn't be. I'd just cut a triangle of 3/8" thick plate and weld it in place. The corners of the shackle plate closest to the handle need to taper off to distribute stresses and prevent braking where the current cross bars are breaking. 

The photo you post shows this area welded closed so it makes no good sense to make it up out of a number of pieces, it's unsound engineering. 

I could have this jigged up and in production in an afternoon and I'd be fancier but I'd be looking at selling the new and improved model. I'd use two bending wrenches rather than a cheater,  weld then cut in the jig and have the shackle plates ready to drop in the next jig for final welding.  It'd take longer to grind smooth and finish than bend and weld. 

I'm not the only blacksmith, welder, fabricator from a production shop background on IFI, I'm pretty sure we'll have you turning these things out more easily than I described. You'll be a hero. Be absolutely SURE you do not copy the $1,200 model or the patent holders will own you. You MIGHT get away with giving them away but if you sold even one. . . shudder.

Frosty The Lucky.

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Thanks for the advice on the steel rod and what to get.  I will give it a try.  One of the throw coaches we know works for Klein Steel in Rochester so I am sure he will steer me in the right direction.  

Ok so the radius of the curve is .375 so if the length was to be exact it would be 3 x 7.125 + .375 +.375 for a total of 22.125.  Since we are not bending the third corner you only add the radius twice.  I will make it about .50 shorter since the open end has the solid plate on it and those two legs will be 7.00 . 

So if I get it correct the end of the rod 6.75 to the center of the first corner post.  

I am thinking that after I weld in the solid triangle I will put it on the CNC to get a nice curve on the shackle corner and drill the shackle hole dead center.

Now when you say "taper off" for the plate do you mean to cut a filleted corner on the plate?  I was going to use .25 plate and cut a slot in the rod to recess it about .125 and weld the plate and open ends. 

Last year I got decent at using a sewing machine for the first time and now maybe I will learn about bending metal in the proper way.  Or play the lottery and win and just buy everything I ever wanted.  LOL

 

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I would say you are over engineering it, and setting yourself up for problems by machining the round bar before welding, especially if machining before bending.   You are going to struggle to get the pockets lined up.   I do a fair bit of bending and unless I have a lot of pcs to do   I  leave the ends of the bars a little long and trim them to length after bending if they need to be accurate.   If  you are making a lot then  you can do test bends and fine tune your process and eliminate the cutting the ends off.   

 I think you are on the right track with flat bar rather than the tubing but a good weld in that area should be plenty strong and likely even stronger than your plan.   The roundness of the 3/8" bar is helping you with giving a built in weld bevel.  By machining a pocket you have eliminated the built in weld bevel and you just have a surface weld.   Instead I would grind a bit of a bevel on each end of the flat bar where you are welding it to the round bar.   I would probably use 3/8" flat bar rather than the 1/4" so you don't need a jig to center the flat bar on the round bar.  As well it will wear the shackle less.  I suspect a longer bearing edge is why the manufacturer uses a piece of tubing.   Cutting a  filet in the edge of the flat bar will be nice and will help eliminate stress risers but you will need to start with a wider flatbar.  

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Regarding the math for the length of the bar you are using the inside radius. You need to be using the centerline radius of 9/16".  The center line is close but if you want to be exact you need to use the "K factor"  which is variable influenced by bending methods, material properties and thickness , angle bent and radius.  K factor charts are often produced in large shops by doing test bends. Center line will get you close though.

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Greetings Marcus, 

       If you build the jig it's easy to cut the stock longer than after the bends cut the joint flush . No math required ..  You could also use simple shaft locks for the 1 1/4 OD bends.  Easy just 1 hours work .. 

Forge on and make beautiful things 

Jim

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  • 1 month later...

What JNeuman said. When bending steel, always take your meAsurements off the centerline.  The outside edge draws out(gets longer), the inside upsets or shrinks, but the centerline stays the same.

 No machineing needed.

As a traditional smith 3/8" is easy to bend hot or cold with a bending forks, scrollingwrench, and a leg vice.

1:determine your total length

2: find and mark with scribe or centerpunch the center of your length.(I always work from the center, rarely from an end)

3: mark the center of both bends.

4: to your full size drawing or best yet, sample bend, use your forks and scrolling wrench to make your angle and compare it to the same.  Make only one sample bend and match all to this.

 

After a few,you will be right on nearly every time and can do far more in less time than via machining.

I can't tell you just how many drawer pull sets I've made for cabinet makers where the pull has a tenon on each end and they are set to an estution plate.

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