Jeff Barr’s Blog

We made a lot of progress on Saturday. Click to see the picture in high resolution.

First, Stephen finished up the axle:

Here’s what it looks like. That axle holds the big black sprocket, the wheel, and a disc brake:

I machined 4 slots on the motor mounting plate. I didn’t get them positioned just right, and we had to procure a new plate from our friendly neighborhood Metal Supermarket. The new plate is thicker, and we are much happier with the result. Here’s Andy showing off the slots:

Then we mounted the motor to the plate and put the chain on. Stephen and Andy had already mounted the torque converter to the motor. Here are the boys in action:

Finally, we dragged it outside and started it up. The wheel turned, and there was much rejoicing (the full version of this picture gives you a great view of what we’ve done so far):

Two quick items. Here’s a detail of the bearing for the rear wheel:

And here is Steve, about to mill a keyway slot in the rear axle:

And with that, I am off to San Jose for the day.

I went away for the weekend, and the boys made some excellent progress without me.

First they finished up the hole for the neck and welded the neck into place, straight and secure:

Then they used the Harbor Freight tubing bender:

to bend the frame rails up in the rear. There were some tricky moments while they made sure that both of the bends started in the position and ended up at the same angle.

After that they welded in the wheel bearings, and put the rear wheel on to the axle:

We still need to cut off the extra length of axle, and we also need to machine a keyway down the entire length so that we can mount the wheel, the sprocket, and the disc brake on the axle.

Take a step back, and voila:

I must say, this is really starting to take shape. It is actually beginning to looks like a chopper. To you it may look like 5 simple pieces of pipe with a couple of bends, but to me this is a ton of fun, a skill-building exercise, a platform for critical thought combined with hands-on experience, and something that Stephen, Andy, and I will remember for a very long time to come.

The next week should be very interesting. Stay tuned for the next episode.

By the way, please leave a comment if you are following our little project…

We spent a long, exciting evening working on what may be the most crucial joint in the entire mini-chopper. This is where the two frame tubes join to each other and to the “neck” — a short tube which will hold the front forks. There are several challenges here. The frame tubes must be joined solidly to each other, and then a hole must be bored through the joint for the neck. It all seems simple until you try to do it, and find out that there are compound angles and no room for error.

Here is the basic neck joint. It doesn’t look all that amazing, but that’s ok since most of it will be drilled out.

Here is a top view showing the tubing notcher clamped into place and about to drill the hole for the neck tube:

Here is Stephen welding in the support piece shown in the next photo. The welder really is that bright:

Here’s a genuine innovation. When we started to drill the neck hole, we found that the rails would move in relation to the jig. After trying various ideas, we simply welded this piece of angle iron to the upright portion of the jig. It may appear to be mounted on a knife edge, but its really quite solid. We then clamped this piece to the rails and ended up with one solid piece.

Here’s the finished hole, illustrated by our lovely supermodel Grace. It looks a little bit off-center; part of that is the picture and part of that is because it is off-center. A few minutes with the angle grinder will fix this up.

Finally, here is how the neck will fit between the rails. We’ll need to make sure that it is aligned laterally with the frame. We were thinking of using some green lasers (because they are cool and because the beam is visible), but a long piece of pipe may have to do. We’ll adjust the final angle in order to set the wheelbase.

And that’s about it. Next step is to weld the neck in to place, and from there we can really get cranking. We’re pretty sure that this was the most difficult part of the project (famous last words).

Here are some pictures of the jig that we will use to hold the various pieces of the minichopper frame in the proper alignment to each other while we fit the cross-pieces, the rear wheel assembly, and the drive-train.

Note: Each picture links to a high resolution (1600×1200 pixel) version. Don’t bother with these links unless you are on a high-speed connection.

First, here’s the jig from the front. The vertical bar will be used to center the front forks. The jig is made of 2″ x 2″ square steel stock and some angle iron. Our first jig was built of wood, as recommended in the plans that we started from. This didn’t turn out well at all, and we scrapped it. The metal jig is far more precise, and was easier to build than the wood one.

In the background, you can see our tubing bender. The black blob to the right is our 8 HP engine. We are keeping it covered so that it doesn’t get damaged by the metal shavings in the atmosphere.

Here’s a view from the rear. The square part in the center will be used to hold the frame rails parallel. We worked hard to make each of the pieces square, straight, and true. I think we are within 1/32 of an inch right now (this is a lot harder than it sounds). In the distance you can see our mill. This 1100 lb behemoth will be put to good use as we shape the various brackets for the frame.

Here is the jig with the two frame rails securely clamped to the angle iron. We are planning to mount our tubing notcher on the vertical component, so that we can make a very precise joint.

Finally, here is the business end of the mill:

Now that I have figured out how to upload and post pictures to WordPress, the sky is the limit.

For the past 6 months or so, my boys and I have been working to construct and equip a really awesome home workshop. Our ultimate goal is the construction of a mini-chopper, a 3/4-scale motorcycle. We have learned some great skills along the way, we’ve gotten better at thinking through engineering problems before we cut or weld, and we are having a lot of fun along the way.

As always, there are plenty of online resources to help out. So far we have purchased the following tools, plans, and books:

• DeWalt Angle Grinder. Very handy and very powerful. Don’t go cheap on this; the lesser imitations have plastic gears that will melt (at least this is what the DeWalt factory rep told me at Lowe’s). This one has been through some heavy use already; it generates some heat but works like a charm.
• Millermatic 175 Welder - This is a fairly heavy duty unit, but I wanted it to last a lifetime. Runs on 220 volt power. As my son Stephen pointed out, this discourages people from borrowing it.
• - Welder’s Handbook. Somewhat useful, makes welding seem a bit harder than it really is.
• - Home Machinist’s Handbook - Lots of very handy tips for measuring and cutting.
• - Atomic Zombie’s Bicycle Builder’s Bonanza - Although this is mostly about building customized bicycles, most of the construction techniques are applicable to the mini-chopper as well.
• Brake and throttle parts from Lawnmower Doctor via eBay.
• Steel from Everett Steel.
• Stephen also bought the engine and a torque converter online; I don’t have the URLs handy.
• Mini-chopper plans from Solution Design, via eBay. This book includes plans for a frame jig built from 2×4’s. We tried that, and it was a huge waste of time. We ended up a building a far better jig from 2×2 square steel stock.
• A tubing bender from another eBay seller.
• A milling machine, from a friend. This is an 1100 lb. behemoth.
• Assorted files, gloves, and safety goggles.

So far we have built a really good frame jig. I will post some pictures in a day or two. Now that we’ve built this great jig, construction will go pretty fast.