Tuesday, September 22, 2009

How To: Mounting Bracket

I thought it would be cool to do a little instructional post on how to build a light weight yet super strong mounting bracket. You can use these anywhere you might need to mount something to the frame. I am using these to hold my electrical box under the seat on my bike. Unfortunately I did not get photos of how i developed the pattern so I will briefly describe the process.

What you will need to get started:
- sharpie
- card stock
- ruler
- circle template
- x-acto knife
- 18g or 16g sheet metal
- tin snips
- drill and drill bits
- welder
- file or grinder

Here we go, making the pattern is the most important part of the equation. If you start off with a crappy pattern you will most likely end up with a part that doesn't fit properly, so take your time and don't be afraid to toss your first few.

First step - Securely locate the object to be mounted. You have to be able to repeatedly measure your object to be mounted. If your stuff is moving all over you won't be able to measure worth a damn. In this case I took my electrical box and spaced it off the frame with a piece of 3/4 in sq. tube. after determining the desired height and back bone spacing I taped the box to the bike and made sure it was not going to move.

Second step - You might want to roughly sketch out how you want your bracket to look. After determining what it is going to look like, measure the distances to your mounting points. Grab your card stock, I always start by drawing a center line down the card stock. Plot your hole locations on the card stock. You can cut, tape, punch , trim your pattern until it fits on the bike the way you want the finished bracket to fit. I physically mount the pattern to the bike like I would the finished steel bracket. Don't forget to add material to your pattern for your bend radius. I usually add 1/16in per bend on 18g-16g. After developing the pattern I usually trace it on to a fresh piece of card stock since by this time the first pattern is pretty haggard, that brings us to the first photograph.

Step three - After developing a good pattern it is time to transfer the pattern to the steel. (keep these patterns in a folder so that next time you need to mount something you don't have to develop the same pattern) I usually scribe the lines onto the metal with a pick. I use a pick v.s. a sharpie so that the dimensions don't get out of tolerance because of the width of the sharpie tip. After the scribed lines are layed down I go back over them with a straight edge, circle template, and a fine point sharpie. Mark your bend lines so you will know where to bend the flaps up. Get in the habit of marking the bend lines with a dotted line so you don't mistake it for a cut line. I am bad at dotting my lines but it has bitten me in the ass a few times. Mark your hole center and center punch them so that your drill doesn't walk around. I added 2 more holes because I decided that I wanted to add some style with some swedged holes.

Step four - You have your pattern transfered onto the sheet metal. Drill all your holes before cutting anything out as this will really save you a ton of hassle and will save you from cutting your fingers off when a bur forms during drilling. You might notice I drilled holes in the corners along my fold lines. By drilling these areas you are relieving the material that will want to bunch up during bending. This will make your bends super clean and it will deter the bracket from cracking down the road. At this point you can go ahead and cut out your bracket from the sheet metal. Clean up all your holes and file the edges at this point, doing this will save you tons of hassle down the road.
Step five - Bend along the lines indicated on your pattern. You can use a break of some times on a part this small you can get away with duck bill pliers. Test fit as much as possible. If there are any fit issues its best to correct them as early as possible. If all is going well you will nail it on the first shot.
step six- After bending and test fitting weld your seams, I prefer to tig weld all my stuff but there is no reason you couldn't use a mig or oxy acetylene. I don't like the idea of solid mounting stuff if I don't have to. There was a set of these rubber isolators laying around the shop so I designed my bracket around them. you can pick these up all over, try McMaster Carr.

Step Seven - Metal finish all your welds. This step is optional but come on - you made it this far so don't cop out. Metal finishing is where you grind, file, sand all your welds so that it looks like there was never a weld in that area. Don't grind too far though or your bracket isn't going to last long before it cracks.

Step Eight - Tack the bracket in place. The point of a tack is to give you a chance to do fine adjustments to ensure that you are happy when the finish welding is complete. With that being said, if after tacking you aren't happy just cut that shit off and make sure its exactly where you want it. I usually do one little tack in the corner then get out the digital protractor and double check everything. When you are happy with your part location tack all four corners then lay down your finish weld.
Step Nine - Pull back and admire the bracket you just pulled off. This isn't the easiest way to mount a battery box, oil bag, or electrical box, but it will last if done properly and it looks pretty cool in my opinion. Thanks for taking the time to read this, and good luck.

3 comments:

MUTINY said...

Thank you! Great post!

thaichopper said...

yeah bro... loved the post.... trying to teach myself TIG.... i,ll make some brackets soon..i hope

andy said...

great! get a book on tig welding and lay a ton of practice beads. you wont regret the time you spend praticing. oh i just found this site called weldingtipsandtricks.com it has some great info on it.