It’s a very good point. Is there any way to compare them fairly? The teflon guides come in some pretty high load ratings. I’m wondering about their durability - particularly when reciprocating over the same path 100 times per second, the way CNC’s tend to operate.
It also brings up the question of how long the linear bearings with internal ball carriages last?
The teflon could wear out faster, but in that case only the bushings themselves need to be replaced, not the rail nor the carriage. If it were a stainless rail, the whole rail has to go because the carriage cannot be removed from it, making replacements much more expensive.
The McMaster parts I don’t think are easily serviced to replace the teflon pads, but can’t check that for you, we discarded the assembly tool that used them. It might be fairly straightforward to modify them so that you could preload the pad with a screw, i.e. take-up any wear…
Well, been busy at work with final stages of a new R+D project…but did manage to locate the teflon guides that I’d bought some years back…they got repurposed into a leak testing machine.
The teflon (actually hdpe?) pads are definitely worn, and the carriage they support would wobble if not for the relatively rigid pneumatic cylinder rod tied to the carriage. The pads are screwed to the aluminum bracket, and so it would be pretty simple to replace them. I think it would also be pretty simple to tap a few extra holes, and use them to push the worn pad down to make contact with the rails (adjusting for wear, like brass gib strips on milling machine ways). Would require loosening the mounting screws and farting around back-and-forth tightening…but manageable.
That’s the level of refinement I’m expecting - it’s a DIY router after all. I may resolve to get a short piece of this track and a carriage to experiment with. If it works well, the short piece may prove suitable for the Z axis carriage anyway, saving maybe 1000 dollars for the X-axis alone. And if I find a flaw, then I don’t have to use it, with small loss for a couple of feet of track compared to the potential gain.
Update:
I received Slocum’s book last week. It is excellent. Everything I need to know - or more.
I am 2 chapters in and I’ve discovered a lot to refer to already related to the questions I’ve asked here. This will take some time to read and absorb (700 pages).
The publisher of this book (SME) does not have an Amazon store, and ships directly to customers using parcel courier service only. So while the shipping rates from UPS are a little higher these days, customs fees between Canada and USA are RIDICULOUSLY HIGHER and I only found out when the broker’s fees hit me. So by ordering from SME directly, I ended up paying about as much as the over-priced used copies on Amazon anyway.
Even though I didn’t order it from there, here’s the review I posted on Amazon:
I am very glad to have purchased this book. This is more than just a how-to guide, it is a Magnum Opus of Slocum’s design and teaching career. The subject of precision machine design requires a multidisciplinary method that combines mechanical engineering, electrical engineering, mathematics, and common sense. Slocum has synthesized all of these subjects in great depth. A complete reading of this book can also be the nucleus of an engineer’s understanding of a much larger variety of engineering subjects, such as instrumentation, metrology, materials science, and dynamic analysis.
My only regret is having found this book so late in my career. It has taken me 20 years to accumulate experience and knowledge to equal only a handful of the chapters in Slocum’s book. Now I can go much further.
Haven’t posted an update in a while. It took some thought, but it became clear that making my own CNC router table requires me to have certain equipment in my shop to make the necessary parts. There are many parts to be built, and it would be dreadfully expensive to have them all made by somebody else’s shop. It would cost more than just buying a CNC table!
Looking at my shop, I have plenty of basic fabrication equipment, but not the kinds of metal-working equipment that permits accurate work. To do this right, I will need a lathe and a vertical milling machine.
This weekend I found the lathe I need. Installing this and setting it up will take some time. It will also involve getting much more equipment than I have (such measurement tools) but I’ve decided that this is the kind of commitment I want to make.
As for this project, it has taken a back-seat, but for a specific reason. I want to return to it before not too long. I got far enough into my CNC router design that I realized what kind of fabrication abilities are needed to build it. I need a lathe like the one I just got and a milling machine like a small knee-mill in order to make the range of parts that a CNC router would need. Brackets for drive motors, end plates and corner joints for the gantry structure, shafts and couplings, shims and so on. While it is possible to have such parts made by a real machine shop to stay focused on the router project, it’s counter-productive when the goal is to add to my manufacturing ability and knowledge.
Steve , I found this Router on the internet recently . Maslow (maslowcnc.com) It operates more like a panel saw than a table router. The biggest advantage to me is, that since it angles up against a wall it does not take up the room that a flat table does. I only have 940 sq., feet so a flat router table will take up far more room in the shop than I want, especially when I have a couple of fuselage and wing sets in there . The router is 8x4 . but it can be upsized to 5x10 . The machine shown in the first video was the original prototype and several improvements have been made to it since then. Bear in mind that this machine is not quite as accurate as a flat table machine but when run slower it will cut alumium , as well as plywood The later models also have a Z axis so they can do 2 1/2 D cutting.
@SparWeb Have you considered chain drives for the long travel on the duplicator?
One of the videos of the Maslow machine shows the chain wrapping on the sprocket.
I suggest that this may be the result of a tiny mismatch between the chain and the sprocket, not enough chain tension or a combination of the two.
In a wrecked auto there are a number of small gearhead motors.
Electric windows, electric seat adjustment.
Worth a thought.
Yours Bill
@Berkshire that does look nice.
There are some projects like an Adirondack chair and a “telescope” chair that I’d like to make and this would do nicely.
“Telescope” chairs have a substantially adjustable height to allow you to look through an eyepiece when the telescope is in many widely varying orientations.
@WaRoss,
I am considering that, indeed. For the duplicator it doesn’t need to be elaborately controlled. Just a momentary rocker switch to go forward/back would do. Yes, a wiper motor would be all I need.