December 28, 2011

For those of you that have been following along, you will remember that the X rail for my old ULS-M25 is badly warped from the fire. To replace it with an official part from ULS will cost me $365 + taxes [or about $13.50/inch for the 27 inch extrusion]. Needless to say, this is a unpalatable price for an aluminum extrusion. So I’ve been trying to come up with possible replacement solutions that are more cost effective. The first step was to create a CAD model for the existing part to serve as a reference. While my model isn’t exact, as it is based on measurements of the damaged part, it should be close enough to serve its purpose.

One option I’ve been considering is using makerslide [store.makerslide.com], an open source rail system. This will also be considerably heavier than the original, and it will also require a fair amount of re-engineering of the remaining mechanics… but nonetheless a valid option to think about. this is certainly what I’d strongly consider use if building a system from scratch. The biggest detractor right now is availability, it is new on the market, and is currently unavailable outside of the kick-starter investors that helped to launch it, which basically locks me out for who knows how long.

One of my first thoughts was to use some standard aluminum extrusions (I may have mentioned this in an earlier post) that you can get at your local hardware store, or metal supplier. I came up with a combination that would do the job, but would weigh considerably more than the original, and likely complex to assemble and get dialled in, as several pieces would be involved.  It would also still require a certain amount of CNC machining to make it work.  It is basically two consecutively sized standard U channel extrusions that are epoxied together at the desired offset, and then the edges trimmed down, and grooves machined in.

At this point I started thinking that if I was going to have to do some level of CNC machining, I might as well explore a totally CNC machined solution. So I designed up a rail, keeping all the critical grooves and maximizing material thickness [for rigidity], while keeping overall weight in mind. What I came up with is a traditional truss structure, with the critical rail grooves running along the spines on the top and bottom. This has the added advantage of being totally open, so replacing the X belt would be easier.

The reference part comes in at 277g according to my CAD package. Which should be pretty close, though I have not tried to weigh the original part I have.
My version comes in about 20% lighter at 222g. [weights based on 6061-T6 Aluminum]

While mine is lighter, it may not be as rigid, though I did try to address that by maintaining a thick spine in my design. I still need to run some finite analysis on the parts to compare their rigidity. Unfortunately the analysis will need to wait until later, when I can run it on my machine at work… It is a very computationally intensive process, and will take forever and a day on my laptop. [I tried and it eventually crashed the virtual machine Windows runs in]

CNC machining isn’t free, or cheap either, so in reality my solution is likely to be more expensive than just buying the part. Having said that, I am lucky in that I do have some contacts with CNC machines, and they may be able to run the part for me, at little more in const than the material itself.

In my process of exploring options, I also searched out aluminum extruders to see if I could find the profile being used, or something close enough to work. Unfortunately I didn’t find a suitable profile. I did, however, find a shop [quite possibly the shop that makes the extrusion] that specializes in small profile extrusions, and they have no minimum order, which means I wouldn’t have to buy 1000lb of extrusion. The tooling costs seemed quite reasonable, but would still run around $1500, putting it way out of the budget, but something to keep in mind for future projects.  However, in the process, I also learned about the process of manufacturing extrusions and one interesting fact came out in my search that I was not aware of. Aluminum extrusions warp quite a bit from the uneven cooling during manufacture, and they are then stretched back straight in a final process. This gave me an idea… perhaps I can stretch my profile back to straight. This would certainly be the cheapest solution, and should be totally DIYable, provided I can acquire the right tools and jig to do it. Given that this option is very low cost, even to explore, I think I’ll try this as “Plan A” and then fall back to the machined solution as “Plan B” with biting the bullet on buying a new extrusion as “Plan C”. I’m ruling out the the two options as being too complicated, and having too many unknowns in the final outcome.



  1. Perhaps OpenRail doubled would fit your needs?

    • I am aware of OpenRail, but thanks. Indeed it is an option, and would have been mentioned in my post had it existed at the time I made the post. Even MakerSlide [which is the inspiration for OpenRail] was in its infancy at the time. As with anything, wait long enough and more and better solutions will arise 🙂

      As expensive as it is, I decided to go with the replacement part from ULS. I decided in the end that altering the moving mass was going to introduce too many unknowns into an already well engineered system, meaning it will likely take me a lot more work to get things running smoothly again. If desigining from teh ground-up I would certainly have MakerSlide and OpenRail at the top of my list.

  2. “I decided in the end that altering the moving mass was going to introduce too many unknowns into an already well engineered system”
    I agree there. Sometimes your just better off with the original part then spending a week on trying to get something that does not fit, to fit 🙂 Thanks for the reply

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s

%d bloggers like this: