Replacing steel & lmxuu with aluminium & plastic

Hi !

I currently have a prusa i3 box frame with "standard" 8mm steel rods & lm8uu bearings. And now i'm hungry for more

I started to look at the Mendel Max 2.0 and see what kind of solutions they have used. And especially how the linear motion for the axes has been constrained.

If i saw correctly, the Y axis is taken care with steel rods and bronze bushings. Sounds good.

For the X & Y axes , it seems that the design is based on a aluminium extrusions (in this case formed to serve specially as a rail) and the sliding parts are plastic ( also special parts designed to be used with linear rails). And those parts require a "special" dealer to provide those. So definitely not availbe to everybody, or at least not for reprapper price

But it seems clearly that aluminum and plastic may create a working combo for linear motion in repraps.

Why wouldnt we change the approach in general to use aluminium for linear support instead of steel rods, as it seems to work fine ? The Mendel Max 2 X & Y axis are based on a rigid misumi extrusion that just have bolted on separate rail. That idea could be utilised in other machines also, and if the "dedicated" rails could be subsituted with something more common, the availability and price would be improved.

At least in our hardaware stores there is much easier and cheaper to find various sizes of aluminium extrusions that could be used for rails than staight smooth steel rod. Yes, the aluminum extrusion definitely are not designed for being rails, but as we have capability to print nylon or pla bushing in various shapes, then the extrusion shape should not present any problem. For example the Mendel Max 2.0 X carriage seem to roll on a two simply slotted extrusions.

[www.igus.de]

The aluminum extrusion would give the benefit over the steel bars that twe could use shapes that are more rigid compared to the weight so that the starightness would be mainteined even though not adding too much weight. And we would have no risk of getting cheap and noisy lmxuu:s in our machines... (Are there silent lmxuu:s in the world )

But am i missing something ? Are those "dedicated" rails more harder on surface so that they can last the use better than "normal" extrusions ? I do beleieve that dedicated rails are definitely straight, but is there too much tolerance with "normal" extrusions, though they seem to be quite straight ?

so ive actually got a set of lm8uu equivalent drylin igus bearings and they are great for the z axis, but they are not as good as the openrail/vslot bearings that i now use, the vslot bearing wheels are quick quiet and accurate. so in short the drylin are very good for the z axis but not as good as a ball bearing wheel on the x and y axis.

But if i have understood correctly the MM2 uses those drylin bearings just on for the x&y. And at least according to the marketing, that should give superb speed and accuracy. Only "problem" is that those rail parts are not easily available, and idea is to substitute dedicated rail and sliding part with "common" but rigid extrusion and custom printed sliding part.

There is a thread on here somewhere about someone using printed parts (PLA?) along aluminum extrusion to act as a linear rail. It seemed that they got some pretty good results.

---

greghoge.com

HUGE 3D PRINTER PARTS SALE!!!

Quote
gmh39
There is a thread on here somewhere about someone using printed parts (PLA?) along aluminum extrusion to act as a linear rail. It seemed that they got some pretty good results.

This thread?

Quote
ddseeker

Quote
gmh39
There is a thread on here somewhere about someone using printed parts (PLA?) along aluminum extrusion to act as a linear rail. It seemed that they got some pretty good results.

This thread?

Not that one, but it was a lot of the same people in the discussion. I'll see if I can track it down in my history.

EDIT - This Thread

Edited 1 time(s). Last edit at 01/20/2014 05:23PM by gmh39.

---

greghoge.com

HUGE 3D PRINTER PARTS SALE!!!

I'm here am just moving from PTFE-lined push-fit bearings to LM8UU because I feel there is too much play in the push-fits still and I cannot print straight enough to achieve a perfect fit.

Later on I will mill a tube to accomodate the push-fit bearings, with an OD of 15mm, the same as the OD of LM8UU. This is needed to make sure the push-fit bearings are aligned since this is very hard to do well with printed holders.

If I had the money I would go for drylins, but sad enough, when I buy them from our Dutch supplier, the Drylins cost a fortune a piece. It's just not worth it, while there are similar much cheaper solutions that give about the same quality.

Well now we are talking

The link gmh39 presented had just the ideology that i'm looking after. There are few interesting concepts, like the Emmanuels printed PLA parts that fits directly to 20x20 extrusion but especially the uGen:s model which fits to bare square tube and is both adjustable and has dedicated material for the glide surface. Is it already in thingiverse ?

After looking those ideas, now what are those benefits that make lmxuu based rails better compared to such designs ? One thing might be incompatible materials and excess wear due to that, but it seems from the examples that it can be taken care of. And is there any evidence, which is better in friction and wear, anodised aluminum or no ?

I think that for same cost it is much easier to get more rigid rails from hollow aluminium than round steel bar, though i have no "scientific" proof of that, just a good old "strong oppinion" And as the MM 2.0 has gone to that approach, there must be some benefits compared to the "common" way. (and definitely added cost if using specialised parts...)

lmxuu bearings and rails provide most consistency in fitment. yea, sure you might get the odd bearing that has a bit more slop or is more noisy, but overall it is easier. You just buy bearings/rod and assemble.

The PLA printed parts require precision dimensional accuracy. If there is like a millimeter of slop in your slides, it will affect your print quality. So you need to print your sliding parts out on a highly tuned, highly precise printer.

---

greghoge.com

HUGE 3D PRINTER PARTS SALE!!!

Quote
gmh39
lmxuu bearings and rails provide most consistency in fitment. yea, sure you might get the odd bearing that has a bit more slop or is more noisy, but overall it is easier. You just buy bearings/rod and assemble.

The PLA printed parts require precision dimensional accuracy. If there is like a millimeter of slop in your slides, it will affect your print quality. So you need to print your sliding parts out on a highly tuned, highly precise printer.

Not to mention that the printer also has to be almost perfectly square!

If your linear rods aren't a 100% straight and square, most bushings and PLA printed bearings will be banding a lot. With LM8UU/LMXUU it's less of an issue.

Today I am going to mount my new X-end system, I can let you know how the experience of replacing my PTFE-lined bushings with LM8UU linear bearings feels. I expect a relief LM8UU bearings are underrated because most people try to get them the cheapest and they end up with crappy bearings. Same goes for people who save on linear rods and don't buy hardened/hardchromed rods. It will decrease performance a lot. I notice it with my old printer, it has shitty rods and shitty bearings, I didn't realise it before, but now after 9 months of use, the printer has grinded it's rods terribly and the LM8UU bearings were cheap and some even lots a few small balls...

When I redo the printer I'll be sure to get better hardened rods and better LM8UU bearings. (Like my 2nd printer has!)

Edited 1 time(s). Last edit at 01/21/2014 10:56AM by Ohmarinus.