How it’s Made: Frame and Fork Alignment Gauge
First, a quick update on the tools that I listed in my last post.
Frame and Fork Alignment Gauge: Interest has been much higher than I anticipated. I thought I might sell 10 of these this month, and ordered material for around 20 just so I wouldn’t have to visit Online Metals too frequently. It turns out that wasn’t enough, and at this moment I’m out of material. I’ll make another batch in a few weeks. I’m keeping track of backorders and sending out invoices to buyers as I have the gauges made. Hahn Rossman (who bought the first one) took a good set of photos of the gauge in his and posted them on his flickr. I’m likely to raise the price on this by $5 to $10 soon, but that won’t affect any outstanding orders.
Fork Fixture: The prototypes are sold and will be shipped out soon (hopefully this week). I’m going to scale back the kit to only include the parts that I make or modify or which are hard to source. I’ll probably sell that kit for $90 (so $100 including shipping). The buyer will need to source parts (including the 80/20 extrusions) from two more sources for about $60 and a dummy axle from Anvil, making the whole thing around $200. Selling the fixture this way makes my life easier (less inventory to manage) and keeps prices low, at the cost of a bit more hassle for the buyer. For the intended market (hobbyist builders) that is the right thing to do.
Now onto the actual subject, how I made the Frame and Fork Alignment Gauge. These are made on my Taig CNC Micro-Mill and I took some photos while making a few of these today. My mill is a small “toy” compared to the large scale CNC machining centers used at places like Anvil, but it is a lot more affordable and still allows me to make projects like this.
I designed the part in an inexpensive CAM package called CamBam. I use CamBam to both draw the basic shape, and then to produce "G-Code" which is what tells the mill how to produce the part. There are 3 basic steps in this part: Drill mounting holes, Engrave Text, and Profile (carve) the part.
I made this fixture plate which locates and holds the material as the cutting takes place. It is mounted to the table of the mill.
Raw material (4" wide by 0.25" thick aluminum) is cut from 6' lengths down to 290mm lengths on the bandsaw. These inexpensive bandsaws are sold by many importers. They aren't very accurate, but they work well for this application and save a lot of time compared to cutting stock by hand.
The raw material is placed on the fixture plate and clamped into place. There are 3 aluminum "buttons" at the top and left edges which are used to roughly place the material. It only needs to be accurate to within 2mm, because the whole edge will be trimmed by the mill when the part is profiled.
A 3/16 2-flute "drill-mill" is put into the mill's head. This is used to drill the mounting holes and to engrave the text that is on the surface of the part. It looks like a normal drill bit, but it is designed to cut both in down and side operations (normal drill bits only cut in a down operation). It is made of solid carbide. These bits aren't cheap, they cost about $10-15 each.
The 4 mounting holes have been drilled and it is now engraving the text. The mounting holes are 8.5mm, but can be made with this much smaller bit by moving the work under the bit as the bit is lowered into the work. That blue stuff is coolant which is continuously recycled and pumped through that nozzle to blow chips aluminum chips away and to keep the tool edge cool and well lubricated.
The text is engraved and the holes are drilled. Time to change the clamping and change the toolbit.
Clamping bolts have been inserted into the 4 holes, and the perimeter clamps and locating buttons have been removed. This makes it safe to remove material for the outside edge of the parts.
The toolbit has been swapped out for a 1/8" 2-flute endmill
The control software (EMC2) has been waiting patiently for me to change around the clamps and to swap the toolbit. Time to press continue and let it do the second part of the job. The purple lines show paths that the cutter has recently followed (so all of the engraving) and the white lines show the full path that the cutter will follow.
The left part is being cut into it's final shape. The toolbit spirals around the perimeter to define the shape, removing 1.25mm more material with each pass. It is moving at 30 inches per minute (800mm per minute) and the bit rotates at over 10k rpm.
The left gauge is complete, and the machine is moving over to cut out the right one.
Both gauges are complete. Now it is just time to remove them from the fixture block and to brush off waste bits and swarf (the aluminum "saw dust").
Once they've been cleaned and the coolant has been rinsed off I put them into the pile of widgets that is ready to ship.
This is what the machine looks like while it is in operation. It is pretty well enclosed to keep coolant and swarf from spraying all over the basement. The cart has a footprint of roughly 4' wide by 2' deep. This is a tiny CNC machine compared to what would be used in industry (and is less rigid and has less features, but costs far less too).
The machine runs for about 20 minutes to make two gauges, and I spend a few minutes in the process dealing with clamping down the material and changing cutters. A larger CNC machine would allow me to make 10 or 20 of these at one time, saving a lot of time on tool changes and allowing me to clamp more material in place then walk away for an hour or more while it gets work done. It would also be much more rigid, so the cutter could cut the full depth of the material at once instead of making multiple passes.
On the other hand the Taig CNC mills start at about $2000 (including the controller hardware, but not the PC), which is pretty incredible considering what can be done with them. I’m using projects like this one and the fork fixture to help recover some of the costs from purchasing the mill in the first place.
I also have a long video on Youtube showing the mill in operation when cutting parts for the hinge on the fork fixture. In that one you can see what the machine looks like in operation and a different style of fixture plate.
I applaud your enterprise and skill. I have read the above but I am at a loss to know what the fixture is for. Please advise.
dennis mac
Dennis: There are some photos of it in use at http://tools.alexwetmore.org. It is a way to check that the dropouts on a bicycle are centered to the seat tube or downtube on the bike. It is used in conjunction with a height gauge and alignment table.
I”ve been interested in getting a Taig mill. What do you think the real world accuracy has been with this mill in terms of positioning and backlash? Did you find you needed to modify the mill at all for increased accuracy?
Daus
Around 0.001-0.002 is pretty easy to get for accuracy and backlash. I didn”t modify anything. The anti-backlash nut used on the CNC mills is pretty easy to adjust.
How has your experience been with EMC2 being in a Linux environment and CamBam being in Windows? Did you use two different computers for each program or dual boot? I was wondering if going to Mach3 would be more convenient as it is all in one operating system.