Linear Rail Hollowing Rig

[Tymur Kharkivskyi]

Hello everyone,

I’d like to start a discussion about a project I’ve been obsessed with lately: a Linear Rail Hollowing Rig. When I first saw Alan Trout’s system, I was blown away by its precision and stability, and I knew I had to try building one myself. I’ll be the first to admit — I’m still gaining both life and technical experience. But I’m a firm believer that if you don’t try and you don’t make mistakes, you’ll never truly learn anything. So, this is the beginning of my journey into precision hollowing. I’m here to learn, so please — criticize my ideas, share your advice, and speak your mind. That’s exactly why I’m starting this thread. I don’t know the exact specs of Alan’s original build, so I’m reverse-engineering it and looking for the best available materials.

Let’s start with the base for the guide rails. I’ve been weighing three options:

1. Steel (Heavy and rigid, but requires precision welding and surfacing).
2. Phenolic/Textolite (Great damping, but can be expensive and tricky to tap).
3. Aluminum T-Slot Plate/Profile (Excellent geometry and ease of mounting).

I have made my choice in favor of aluminum, and I will be mounting the guide rail to it.






I have started selecting the diameter for the shaft. I was choosing between three options: 40, 50, and 60 mm. The 40mm seems a bit flimsy, while the 60mm, on the contrary, feels heavy — I am concerned that the extra weight will kill the guide bearings, although the sellers say they can withstand a lot. I settled on 50mm, but I am also making one for 60mm in parallel. For the guide rail, I initially took a size 20, but then switched to 25. For the 60mm bar, I will need at least a size 30 rail.

 

[Tymur Kharkivskyi]

Moving on to the shaft setup. There is one key element here: the main carriage (holder), which must allow for up-and-down adjustment and rotation around its own axis. In addition to these movements, it has to support the handle, the blade, and the mounts for a video camera or laser guide.

I decided to simplify the carriage by moving the laser/camera mounts directly onto the shaft itself. I’ve commissioned a machinist to cut threads into both my 20mm shaft (for the laser) and my 50mm shaft. I’m a bit concerned that the 20mm shaft might vibrate loose, so I added a jam nut (lock nut) just in case. Better safe than sorry!



I couldn't post a video here, so I had to make an image instead.

Until I assemble the entire system, I am keeping the 20mm shaft long. Once everything is installed, I will cut off the excess. I thought for a long time about whether to choose a laser or video. I read so many complaints about laser systems and lasers failing due to vibration that I decided to try a car rearview camera. For now, I bought a simple $40 version because I didn't know which one was optimal. Trent Bosch sells his visualizer for a lot of money; I still don't know what kind of camera and screen he uses—they must be good—so I decided to try a more modest model for now, a 'beginner' version, so to speak. If I need this system, I can just screw it on top; it won't add extra weight to the carriage on the shaft and hopefully won't get in the way. If I don't need it—for example, if I'm just doing roughing down to a thickness of 1 inch—I can simply remove it so it's not in the way on top.

 

[Tymur Kharkivskyi]

Now we are mounting the shaft to the guide rail via the bearing carriage. We welded a plate to the bar and drilled holes in it, taking great care to weld from the inside so that no seam is visible on the outside. The carriage features M8 threaded holes, and we will be securing it with four socket head cap screws.

 

[Tymur Kharkivskyi]

Choosing the main bearing is probably the most critical moment. I listened to many different opinions and read a lot on this subject.
There were several different options under consideration:



I am leaning towards the second option: using narrow bearings. My plan is to install two of them—one at the top of the carriage and one at the bottom.