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  #1  
Old Wed 11 October 2006, 23:51
Dick van Randen
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One of the things I noticed about the L design is the flex and the possibility of the car to jump the tracks.

Would this design work?

PS. This is not to scale. I just used some of the other drawings as rough guide.



The load in the bearings radial direction now is just the mass and should be steady.

The axial load should be stiffer and prevent the assembly from racking.
  #2  
Old Thu 12 October 2006, 03:41
Gerald_D
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Dick, I don't think that the L-design is bad at all. It has been used for years as a very economical rail. (From steam crane days!). You are right in that the L can twist easily, but a good support under the rail will prevent that.

What you sketched is good, and similar to the z-slide. But it is expensive to get those two edges of the flat bar parallel to each other, and to hold them parallel as they wear with time. In this configuration the rail should be hardened. I also wonder if this rail would self-clean properly?
  #3  
Old Thu 12 October 2006, 07:00
Dick van Randen
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I know what you mean by wear, the rails wear and create a hook on the edges(like a wood scraper) from the wheels rolling back and forth.
The section the wheels would roll on would have to be hardened or have hardened edges mounted , like the ones Hepco supply.

I knew I'd seen the design before, I must have Z-axis of the brain... time for a realignment.
  #4  
Old Thu 12 October 2006, 09:12
Mike John
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It appears to me here that you now have the entire load on just one wheel in a pair,the upper wheel, whereas in the 'traditional' method the load is spread between the pair of wheels.

.....................Mike
  #5  
Old Thu 12 October 2006, 15:34
Dick van Randen
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Yep,

but I would happily add more V bearings if it resulted in a better design that would be within the realms of my skill and resources.

Geralds comment about laser cutting has me chewing on an idea. Can you laser cut angled metal or does it have to be flat?

D
  #6  
Old Thu 12 October 2006, 22:36
Gerald_D
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Our laser-cut supplier will not cut angled metal, I'm quite sure of that. He already tells me that a part which is starting to fall away from a cut, and starts to lean, bounces the laser off at an angle and causes some of the marks that we complain about. Also, realise that a laser does cause some distortion because there is some heat input - much less than with plasma cutting, but not zero.
  #7  
Old Thu 12 October 2006, 23:04
Mike John
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Am I to assume water jet cutting is a no-no?

...........Mike
  #8  
Old Thu 12 October 2006, 23:14
Gerald_D
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No-no

Meaning that it doesn't have to be a no-no

But it depends on what Dick wants to achieve...?
  #9  
Old Fri 13 October 2006, 01:09
Dick van Randen
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I was hoping that parallel or near parallel 45 degree edges could be laser cut in high carbon steel, the end result would be edges for the roller bearing to ride on that were close to parallel and hardened all at the same time. ( In order to do this the metal would have had to be tilted 45 degrees)

Back to my over crowded drawing board.
  #10  
Old Fri 13 October 2006, 01:24
Gerald_D
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The laser face (if 45 deg were economically possible) is not smooth enough for a roller and will need some grinding to clean it up. The laser-hardened skin is very thin and probably won't withstand the grinding.

But, if the beach sand is too soft to drive on, get a bigger & wider wheel.....

And that is what the MechMate has. We have 6mm wide rails compared to the original 4.7mm and the mean roller diameter is now 38mm compared to the original 28mm. So far the rails look very healthy with no signs of "burring". (didn't even drop the tyre pressure! ). Although it is only a year old, I'm optimistic that it is a very good long-term solution....and economical.

For the z-slide, I am surprised that nobody is offering hardened slides as an after-market accessory in the home market. If I were to try and sell them from here, the cost of shipping would kill the price. There must be a gap for this, but ShopBot could announce their own hardened slide at any time. (I wouldn't add BWC rails to a soft slide - I would just make the whole slide of hardenable material. The z-slide is manageably short and one can take a completely different approach compared to the much longer x,y-rails).
  #11  
Old Fri 13 October 2006, 03:16
Mike John
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A supplementary question, as they say at prime Ministers question time!
Can you use water jet in place of laser cutting for all mechmate parts?

I found this on the web.
With Flow's innovative software, waterjet operators are no longer restricted to cutting only on the XY plane, and can easily design and cut parts never imagined on a waterjet with varying height and thickness," stated Robert Peterson, waterjet market manager for the company. In addition, FlowMaster 6.0 will help customers lower cost per inch on projects through the software's ability to improve cut speed and thickness."


.........Mike
  #12  
Old Fri 13 October 2006, 04:42
Gerald_D
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Mike, wajerjet & laser cutting are readily interchangeable for the way in which the MechMate is designed. Around here the laser is simply more common and economical.

Plasma & flame-torch cutting can also be used, but the drawings will need to be adapted for them. With laser/water there can be small tongues fitting accurately into slots (see the y-car parts) - with plasma/torch the tolerance is far too rough. Laser/water can cut finished bolt-holes - with plasma/torch it is better to drill the holes as a separate process.
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