View Full Version : finding EXACT centers

06-22-2013, 06:10 AM
While building a Warrior rear assembly for my Tri-Cruiser it dawned on me AFTER I got it all assembled, a better "mouse trap".
You need to view the plans on building the rear assembly but here is a simpler and perhaps stronger method to assemble. I needed to increase the tire to frame distance so I built this assembly with a wider gap. The attached drawing is different than the plans as it makes the sides cleaner (no caps to weld) except one on the end (green section). The red section is between the two legs instead of on the ends. IMO makes the unit stronger but does it really need more strength? Not really but would make assembly easier.
NOW to get the axle stays ACCURATE and dead center. If you use a metal yardstick (tape measure is NOT accurate) or two sticks held together with spring clamp (old cabinet makers trick), measure from point A to point B (note do not weld at point B or point D yet as the weld bead will cause inaccuracies). The distance from point A / B must be the same as from point C / D.
I found using metric is easier to get dead on vers imperial inches but the two sticks and clamp method is even better. Using triangular measurements is how a cabinet maker gets DEAD ON SQUARE cabinets. Same approach can be utilized in placing a rear axle on the rear of a bike trike or quad.http://i992.photobucket.com/albums/af44/MrDEB/centerrearassy_zpsaac1347c.png (http://s992.photobucket.com/user/MrDEB/media/centerrearassy_zpsaac1347c.png.html)

Hopefully this will make building that bike easier and more accurate.

06-22-2013, 06:55 AM
While that is a very interesting thought. I found Brads method of centering fairly easy per the plans suggestion. It keeps it simple. Plus I don't own an accurate ruler of the length to mount the 36 inch wheel I'm using.

06-22-2013, 07:08 AM
I see you have a Lincoln welder same or similar as the unit I bought off Ebay -- Lincoln Century 80gl?
I took a second look at the method Brad is using which is simpler BUT if the rim is ever so slightly not straight then your axle stays are not EXACTLY center. Don't have a long yardstick, use two wooden sticks and spring clamp. I like the two stick / spring clamp better. No inaccuracies reading measurement. Its either GO or NOT GO.
Am going to build another rear axle assembly for WARRIOR bike project next.

06-22-2013, 08:01 AM
You have missed out the other dimensions that are needed! For you system to work, either lines AC and DB must be known parrallel , or AD and CB must be known equeal, or your system may not line up on center. Sorry but that's geometry for you. You have to measure a triangle somewhere to lock it in shape.
Steve G

06-22-2013, 01:29 PM
The points that you are measuring from (B and D) are referenced from the section that mounts to the main frame (orange section). This example I posted gets the axle stays exactly parallel with the orange section.Using this method will assure that the distance from AD and CB are exactly the same. Locating the exact middle of the orange section is just as easy for when you attach to the frame. A tape measure is not exact. Close yes but exact, no. I initally used a tape and found that the stays were off by 5mm. Using the two short sticks w/ spring clamp is exact. Measuring the triangle will assure that the axle stays are same and parrallel with orange section. I used a fairly straight rim but it dawned on me that the rim has to be PERFECTLY straight but then you must measure at exactly the same point on each side of the rim. The axle stays I tack welded, using a rim were 2mm off. Using the stick / spring clamp method the stays are exactly the same distance and square with the orange section.
After I tacked the rear axle section to the main frame I checked, using two sticks and spring clamp, the squareness from the points A and C to the front spindles in a triangular method= Dead On square.

06-22-2013, 01:57 PM
I see you have a Lincoln welder same or similar as the unit I bought off Ebay -- Lincoln Century 80gl?

Mine is a Lincoln 110 Amp 110V with A-B-C-D amps setting and variable speed pot. Upgrade with a Gas kit to be gas shielded Mig. This was a special Nacar edition put out some years ago- I bought it from a Garage Sale in my Neighbor along with my Dewalt angle grinder. The Guy bought it at a Storage Reclaim Sale Auction- cheap. Thus the saving were passed on to me.

06-22-2013, 08:58 PM
I have read this over many times, and nowhere do you say anything about the requirements any other dimensions than the two diagonals, AB and CD in your sketch.
This is the ideal set up.
This is what could happen if you do not specify that AC must be // with DB, OR that AD must=CB . Either one of these locks the set up.
Your system is correct provided you do this, but you omitted this from the explanation.
May seem obvious, but to any one with no knowledge of geometry, its a trap based on your explanation.
The dimensions are not real life numbers---just came out that way when I added numbers to the drawings!
Then we both missed the point that the two dropout tabs must be identical to place the axle //AC !!
Overall, I think its easier to use the wheel (which should be within 1mm anyway) and continue to use it as reference throughout the build. In then end, on a warrior, it does not matter if DB is not accurate, but it does help if AC is at 90 degrees to the centreline!
The frame is only there to hold all the bits in the right place!
Have fun,
Steve G

06-23-2013, 08:45 AM
I left out dimensions as a set of plans must be purchased to actually build, I thought I mentioned that the axle drop outs MUST be identical.
YES a wheel will work just fine as this is not rocket science --- lol.
Where the DEAD ON accuracy would come into play is for a LONG wheelbase trike. That off center measurement would tend to add some mis-handling characteristics to the trike.
The triangular measuring would aid in getting Steves Mystery Build rear axle perfectly aligned with the front spindle. Even a quad would benefit from this measurement technique.
Only reason I started this thread is to explain how to get / find exact centers / parallelism in a build.
Hopefully today it won't be raining so I can finish assembling my creation for a final test ride before making it look good with paint. Hopefully riding in the local 4th of July parade.
Question - what do you think of my idea of building the rear section as pictured instead of as per plans. IMO it would be less work and perhaps stronger?

06-23-2013, 11:16 AM
As picture you build looks pretty neat. As to strong that remains to be seen. Spinners warrior required a bit of triangular support to reduce flex. I'm fairly sure I may have to add some cross bracing my self because of my over sized wheel on my warrior extended the frame a bit. Turning to SWB to a LWB by the nature of the beast. I may even have to modify to the spirit style instead as the length bothers me a bit. I'm estimating a 24 inch loss of length going that route. But may mock up with a different frame build. We'll see. For painting- but sure to wire wheel all the rust off good. Gracho has some excellent prepping tips.

06-23-2013, 11:20 AM
It probably is stronger, but the forks were strong enough any way, so its not really an issue. Where the gain is that's its easier to keep the joints neater, or in places where its easier to tidy them up.
As to errors in alignment on as long Delta, providing you are only talking less than an inch either way, the only person that might notice is the person at the end of the street--you won't when you are riding! You might notice if it was three inchs out! I see so many here wjth bent frames that are more than three inches out of alignment, and leaning to one side, with three wobbly wheels, I wonder why we bother to measure anything, as they keep riding, under control, everyday, with no worry! A wobbly wheel that does not hit anything is considered straight here!
Have fun,
Steve G