FRAME ARTICLE #4


MORE ABOUT TOOLS: What do you need in the way of tools now that you have built your frame fixture and have the motor installed in the proper location?

Hand tools: I tend to use a lot of 1" OD tubing, in .062" wall thickness or less. Sheet metal at the swing arm pivot and shock mounts will be in the same 16 to 20 gauge range. ( A brief aside - ferrous tubing and sheet are often sold by the standard gauge thickness. The sizes you are likely to use are: 14g - .078", 16g - .062", 18g - .050", and 20g - .037"). For shaping the tubing I use a hacksaw, left and right compound aviation snips, a 12" rat tail file, and a 12" half round bastard file. If you can't cut the metal with snips - IT IS TOO THICK (with some exceptions). The curvature of the 12" half round bastard file is very close to a .5" radius, so it is handy for profiling the tubing. The rat tail file is helpful for quick metal removal prior to final shaping with the 1/2 round file, as well as deburring the inside of the tubes after they have been filed to fit.. Many times you can make two cuts on either side of the tube with a hacksaw that will be close enough to finish with the 1/2 round file. A small ballpeen hammer is also handy where one section of the tube joint doesn't quite come down to meet the other tube surface. A light tap or two can resolve this situation. The closer the fit of the joint, the less movement you will get in the tubes when they are welded, and the joint is stronger too. A solidly mounted bench vise will give you somewhere to hold the tubing while filing. The Eastwood Company (800-345-1178) has a handy bench shear ($90) that operates like a can opener, with rotating wheels. It cuts up to 16g steel and is good for curves as well as straight cuts, and doesn't distort the metal very much.. A Unibit (TM) is great for putting holes in sheet metal, as are chassis punches.

Power tools: A vertical mill with an appropriately sized end mill is very handy for profiling tubing, but pretty expensive. There are some "joint jiggers" available (look in Circle Track magazine) which are an arbor with a hole saw mounted to a plate that allows tubing to be clamped at different angles. The tool is mounted in a vise on a drill press, which provides the power to turn the hole saw. The hole saw cuts the end of the tubing. These seem to run about $160. The hole saws do a nice job, and last a lot longer when you keep the speed and feed fairly slow, and apply lots of coolant. A die grinder with appropriately sized stones/sanding drums can be used for final finishing of the tube. A band saw is handy - but watch those fingers - you know, the ones that used to be attached to your hand. Power shears or nibblers are also handy for cutting out bigger sections of sheet metal. If you are going to use bent tubes try to obtain use of a bender. You can pack the tubes with sand and then heat and bend them, but it is a lot easier to use a bender. Again, Circle Track has ads for benders. Many adult education metal shops have manual benders, as well as lots of other great tools. If you are going to put a bend in the tube, it must be supported by bringing another tube into the center of the bend. Otherwise, it will just bend further when a load is applied. A properly used bend can eliminate several welds, but it must be supported properly.

           O               O
         /   \           /___\
         |   |           |   |
         |   |           |   |
      
          BAD            GOOD
         BENDS           BEND

All of these power tools are wonderful to have, but none of them are required. You will need access to a small lathe for turning bearing cups for the steering head and swing arm, and the bushes to go in the swing arm pivot sheet metal in the frame. It is also handy for making some thick stepped washers for tubular motor mounts. These washers have a major diameter the size of the tubing they will be welded to, and a minor diameter step that is a close fit inside the tube. The small step helps ensure that the weld isn't taking all the shear load on the mount. I like to make them about .25" thick and then take a light facing cut in the lathe after welding. That is when I drill the close tolerance hole for the motor mount bolt. Don't forget to deburr the side of the hole inside the tube. I'll attempt another small drawing - I hope it doesn't get too far out of whack:

   |_|_ _ __|_|     tube
      ______
    _|______|_
   |__________|    stepped washer     

Distortion: as mentioned earlier, you will have to learn to deal with distortion. Try to get all the rest of the frame welded before installing the sheet metal at the swing arm pivot. That way you don't have to worry about welding distortion elsewhere in the frame pulling the swing arm pivot area out of alignment. Here are some things I do:

I use big stepped washers to locate the steering head tube on the fixture. This washers should be a tight fit in the tube, and extend into the tube at least as far as the bearing bushes will. If you are building just one frame, they can actually BE the steering head bearing bushes, but with a small hole to fit the fixture stem. After you are done with the welding take them out and bore them for the bearings. They will help keep the steering head tube from going out of round when frame tubes are welded on. Frame tubes should be attached as close to the end of the steering head as possible to keep the steering head from experiencing bending loads.. Unfortunately, if you put your perfectly sized bearing bushes in first, they often seem to end up distorted after all the frame tubes are welded on next to them. After welding all of the tubes to the steering head I remove the washers and insert the bearing bushes into the steering head. I tack the bushes into the steering tube. The bushes have a flange like the stepped washers so they can be pressed into the steering head, but the flanges prevent the bushes from being pulled too far into the tube. I use a fairly thick bush, that way there tends to be little or no distortion when they are tacked. I usually use 2.5" x 16g tubing for the steering head. The steering head bearings I use are aftermarket tapered roller bearings for the Kawasaki Z1. These bearings have a 30mm ID and a 48mm OD. This gives a near .25" wall to the bush. The bush isn't light, but it is strong and doesn't tend to distort. The 30mm ID allows the use of a hollow aluminum steering stem.

After the steering head is reinstalled on the fixture with the steering bearings and the completely welded tubes (don't forget to weld on your fairing/instrument mount lugs before this), start adding on the rest of the tubes reaching towards the swingarm pivot area. After these are welded on you can add the swing arm pivot sheetmetal. I leave a little play between the hole in the sheet metal and the bush the swing arm pivot pin rides in so that if the sheetmetal moves a little while being welded it won't pull the bush out of location. I like to use a thick (.090 to .125") large OD washer over each end of the bush. The washer ID is a close fit on the bush OD. I tack the washers in place on the outside edge, then finish welding around them. If you are careful, you will find that you have been able to compensate for any earlier distortion with each successive step, and the swing arm pivot bushes will be right where they should be. After I have welded one end of the first bush I will drive out the swing arm pin and re-ream the hole. The end of the bush will be lightly distorted from the welding. Then I reinstall the pin and finish the other end and repeat the reaming process. If you wait until both bushings have been welded you will probably find the pin very difficult to remove. Remember, the bushings must be as close to a zero clearance fit as possible. With tight tolerances, a little warpage has a lot of clamping power.

Once all the rest of the frame is finish welded. I will double check that the motor is still in the proper position, and carefully add the motor mounts that were not at the end of a major frame tube (think of the front motor mount on a bevel drive Ducati twin) to the frame. You can make more tubular mounts, and attach them to the frame with box section sheet metal fabrications. Another technique is to make a flat mount bracket of .080 - .090" sheet. Weld an undersize hole washer on it where the bolt will go through, and drill the hole to size. Then weld a strip of sheet metal around the edge of the bracket, creating a flange welded to the flat bracket and the frame tube. If you make the ends of the flange several inches long where they weld to the frame tube you will usually have sufficient area to spread the load out without needing to put a doubler on the frame tube, or use a thicker wall frame tube. NEVER use a thick motor mount plate welded to the tube without a flange - it will flap back and forth and break the tube. Unless of course you are making something out of 1/4" wall tube - in which case it must not be a motorcycle frame. Another drawing follows:

     ____                _      bolt going into mount showing tapered sheet metal flange
    | |  \      ________| |     The flange is wider at the tube because that is where
    | |   \    |________| |     the stress is greatest.  The flange should weld to the
    | |    \            |_|     sides of the tube, along the neutral axis.
   _| |     \_________
    |________\
  __________________

Now the main frame is basically done. I'll talk about swing arm construction and shock mounts next time, and probably also about why the standard monoshock installation is really not a very good idea.

Until next time - keep plenty of bandages on hand. All that sheetmetal tends to have a sharp edge sooner or later.

Cheers,

Michael Moore

Euro Spares

AFM/AHRMA #364


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