Making Skate Frames

Ever wonder what goes into making your skate frames?

This blog entry shows my process for turning raw billet into top quality skate frames. Very few manufactures work with the solid "billet" of aluminum. Most frames are made from lower strength extruded channels using an alloy that is soft enough to squeeze through a form then heat treated after the channel is created.

Working with a solid billet makes sense for me since I am a very small operation and the up front cost associated with the high volume extrusion process does not make sense given the small number of frames I sell. The process I use also results in a stronger frame and provides flexibility so I can make lighter weight or heavier weight version of my frames if needed. I can also change the layout of the frames to provide longer or shorter frames and move the mounting decks around if I choose without the drawbacks associated with high volume manufacture.

Making skate frames involves machining sequences and manual processes. I start with a solid billet of high strength aluminum alloy. The process of turning this into a speed skating frame involves tool selection, programming of cutting movements, loading stock in the CNC, and precise positioning of the tools and fixtures.

Everything I make is created in my garage behind my house on weekends or the evenings by me working alone. I view the process as a "craft" and am working to make the best skate frame that I can produce.

The first production step is to create four precisely positioned holes in a block of aluminum. Two of the holes are used to hold the block for subsequent operations and the other two allow me to index the block into my fixtures for later operations. The holes used for holding the block are tapped with 1/2 bolts while the indexing holes are reamed at to 4mm size so they will mate with hardened steel dowels that I use for my other operations. In this first sequence, I work with each block individually to set it up in the machine and then make the cuts. One of the most difficult part of making a frame is figuring out how to hold on to the material as you cut it down. By using bolts to hold the billet and index locations to position the frame I have flexibility and do not need to worry about having a machining operation cut through a clamp plus since I index the location of the frame based on the position of the mounting decks I can change the wheel spacing and use the same fixture system for 4x100, 4x110, 3x110/100, and other layouts.

For creating the index holes, the block is positioned on pins so it is always held in the same X,Y,Z position. The following photo shows my Kurt vise with special jaws attached.
















Block in vise.




Block in vise (bottom view).




The height for each tool needs to be recorded before machining can start. When the CNC selects a tool it uses the programmed height to offset movements. If the programmed height is wrong the part and often the tool is going to be destroyed so great care is taken to ensure that the height is correct to +/- 0.001"




I use a drill then a CNC reamer when making an index hole or skate axle. Drill bits never really make perfect holes so I drill a smaller initial hole then use a reamer to expand the hole to the proper size. The reamer is like a drill bit but it has six flutes with straight cutting edges.




At the end of the first part, we have a block with four holes in it. It does not yet look like a skate frame but we are well on our way. Also, since I use these same holes for all my current frame designs and my holding fixture I can make 4x100, 4x110, 3x110/90, or most other frame layouts from this block using the same clamping techniques and fixtures.




Using a hand tap for the 1/2 holes. The tap cuts the threads for the bolts in the hole made on the CNC.





It's a tight fit but my CNC table hold four blocks for the second milling sequence. In the sequence, I machine the left side of the the frames. The blocks are held in a fixture that positions four blocks on my CNC table. Each block is held to a fixture from the underside using beefy 1/2" bolts. If you look close at the photo you will notice that one of the blocks is longer then the other since it will include a brake frame. I also mill out a tiny bit of the long block in the first sequence so I can access a fixture bolt. The shorter frames don't overlap the fixture bolts so I don't need to do this little bit of milling. The second operation has a lot of machining to remove all the material from the blocks. It takes about 3.5 hours of machine time for this stage of the process.

Fixture 2 loaded in the CNC with four blocks.




I start by making holes for what will become the skate axle positions. Each hole needs to be drilled using steps since the material is 1.5" thick. Then I ream the upper part of the hole and use a smaller drill to drill the part for the threaded area of the skate axle. After the axles holes have been formed, I machine the outer profile of each skate frame then machine the side cutouts and finally put a nice chamfer on the edges.



At the end of the second machining sequence the blocks now look a bit like skate frames but they are still solid and only finished on the right side.



With a new fixture mounted in the machine, I can finish the left side of the frames.


Here is a quick video of the chamfer operation.



At this points the blocks look good from both sides but they are solid in the center.


In the fourth operating, I machine the skate frame channel from the top and cut the mounting slots. With this operation it is hard to see what is going on since the frame is locked deep in a vise with extended jaws.

Roughing:


Here is a picture of me taking the frame out of the fixture. You can see how the fixture works and how much of the frame is now finished. The only part that is left to do is to flip it over, machine the underside of the mounting decks, bearing bosses, and bracing.



The fixture for the final operation holds the frame in the vise with the underside exposed for machining.



I mount axles through the holes in the frame to stabilize this area for when we cut the bottom side of the bearing boss.



If you look close at the photo you can see the shape of the bearing boss. I am quite proud of the shape since it is one of the more difficult areas to machine especially when you consider that the hole is made from an earlier fixture and then the upper hemisphere of the circular boss is cut from the top of the frame and the lower hemisphere is cut from the bottom of the frame. The boss is a place where a mis alignment in tool offset or fixture position will show up.

The cutting marks on the metal look worse they they are since the way light plays in the photo it looks less smooth then it really is. After some hand polishing and then anodize the final product will look quite smooth.




As a final step, everything gets inspected to ensure the frame is accurate.

The 4x110 frames weigh in at 217g for the non brake version. The brake version adds 39g.

At this point, the the frames are functionally complete. I still need to hand polish them and they are anodized before they go to the customer.

I did not get any photos of the hand polishing process but I snapped some photos of some frames as I was cleaning them.

Here is a soapy frame as I clean it after polishing.


Inventory of clean frames that need to go to the anodize shop.