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Sheldon Dingwall
Registered
Username: Sheldon_dingwall
Post Number: 9
Registered: 08-2006
| | Posted on Monday, October 30, 2006 - 10:03 pm: | 
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Any thoughts on making the V-rails out of heavier angle. Maybe 3/8" or 1/2"? Something that would resist twisting a little better. |
Gerald_D
Registered
Username: Gerald_d
Post Number: 350
Registered: 11-2005
| | Posted on Tuesday, October 31, 2006 - 05:28 am: |
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Hi Sheldon.
On the moving gantry, the weight needs to be kept down (that's the one reason I trim the vertical part of the angle rail so short). But, the x-rails could easily be heavier. My approach is to stick to a standard profile for both rails and beef up the underlying support if twisting is a problem. However, I'd need to be convinced by a dial gauge that there really is twisting. On our old SB, the bolts in the rails were too far apart for the support to be doing a proper job. |
Sheldon Dingwall
Registered
Username: Sheldon_dingwall
Post Number: 10
Registered: 08-2006
| | Posted on Tuesday, October 31, 2006 - 06:55 am: |
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How are you using a dial guage to measure twist in the rails? Clamp it to the gantry or car? |
Gerald_D
Registered
Username: Gerald_d
Post Number: 351
Registered: 11-2005
| | Posted on Tuesday, October 31, 2006 - 07:24 am: |
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Place the gauge under the gantry and run the car over it? (Havn't done it myself):
Differences in readings between those 3 points is probably what one is looking for.... |
Gerald_D
Registered
Username: Gerald_d
Post Number: 352
Registered: 11-2005
| | Posted on Tuesday, October 31, 2006 - 07:30 am: |
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Or, more practical, only 2 points......
 |
Gerald_D
Registered
Username: Gerald_d
Post Number: 353
Registered: 11-2005
| | Posted on Tuesday, October 31, 2006 - 07:37 am: |
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Something for the weekend....
 |
Gerald_D
Registered
Username: Gerald_d
Post Number: 354
Registered: 11-2005
| | Posted on Tuesday, October 31, 2006 - 08:25 am: |
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Took a quick breakfast break and went to visit the MechMate upstairs armed with a dial gauge....
Parked the y-car to one end of the 1.9m [6 ft]gantry, laid a plank over the middle of the gantry, put the dial gauge under the middle of a cross-tube, Applied and removed a 12.3kg [27 lbs] weight a couple of times. The dial would fluctuate by between 6 and 7 increments of 0.01mm. The flex being average of 0.065mm [0.0026"]
Moved the gauge to under the tip of the angle rail (outside the rack) and the readings mostly fluctuated 6 increments, with a couple of 7 increments sometimes.
Conclusion:
1. Instruments not accurate enough to discern the rail twist factor.
2. The rail twist factor with a 12.3kg load variation [27 lb] is less than 1 marking of 0.01mm [0.0004"] |
Dick van Randen
Registered
Username: Dvanr
Post Number: 28
Registered: 03-2006
| | Posted on Tuesday, October 31, 2006 - 10:35 am: |
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I did a similar measurement on the Shopbot a while ago. I did my measurement between the gantry and the table and discovered something interesting. You get the expected bowing effect as the car reaches the middle and you measure in the middle. However, it all seems to be interacting as the y car mass moves to its extremes.
Y car position
close..........middle.........far
x flex max....xflex min......x flex max
y flex min....yflex max......y flex min
if the maxs and mins cancel out it would seem you could get a flat surface! |
Rob Smith
Registered
Username: Truman
Post Number: 1
Registered: 12-2006
| | Posted on Thursday, December 21, 2006 - 04:31 am: |
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would this work for rails it would allow for some adjustment as well as the use of flat stock which might be easier to put a nice edge on? |
Gerald_D
Registered
Username: Gerald_d
Post Number: 664
Registered: 11-2005
| | Posted on Wednesday, December 27, 2006 - 08:43 am: |
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I don't think that flat stock is much easier to put an edge on. In any case, you are illustrating the problems of mounting flat rails and my approach is rather to spend that extra effort toward getting the edge directly on the angle iron. |
bugmenot dillbert
Registered
Username: Soulvoid
Post Number: 1
Registered: 02-2007
| | Posted on Sunday, March 04, 2007 - 11:47 pm: |
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How about this?
The end plates of the gantry would have to be modified, the shaft of the motor may not be long enough and the support structure would have to be modified. |
DocTanner
Registered
Username: Doctanner
Post Number: 41
Registered: 11-2006
| | Posted on Monday, March 05, 2007 - 02:03 am: |
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The Mechmate as drawn works extremely well. PERIOD
I didn't think the grinding of the angle iron was a worthwhile effort. I was wrong.
The grinding of the angles is not that difficult. I cut mine down to an inch high with a thin abrasive blade.
Then mounted an 8 inch grinder on a 45 degree angle. Passing the angle through like a tablesaw.
Yes, I spent the day grinding away.
My rails are less than perfect!!! But I am pleased with the results.
I am strictly a hobbiest. I was caught by suprise by how many people want things cut.
Use the "Microsoft Method"
Functional ------------------------> proceed
Will it make money as it is? ---> proceed
Can it be upgraded?-------------> proceed
Main goal is to get a functioning machine that will make you money.
Every part of the MechMate can be changed with a little effort.
Perfection should be strived for but it is not mandatory,
DocTanner |
Gerald_D
Registered
Username: Gerald_d
Post Number: 1106
Registered: 11-2005
| | Posted on Monday, March 05, 2007 - 07:25 am: |
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Thanks for that post Doc. You have perfectly captured the essence of the MechMate project.  |
bugmenot dillbert
Registered
Username: Soulvoid
Post Number: 3
Registered: 02-2007
| | Posted on Wednesday, March 07, 2007 - 06:47 pm: |
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Doc,
would you mind posting a pic or two of the setup you used to grind the rails?
I don't know but I think it would be interesting if there was a way of using the 'proper' linear rails with the mechmate allowing choice for the builders. Secondly, I hate any form of cutting (of anything) that involves cutting it lengthwise. |
Gerald_D
Registered
Username: Gerald_d
Post Number: 1123
Registered: 11-2005
| | Posted on Wednesday, March 07, 2007 - 07:15 pm: |
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"Bugmenot", there IS an interesting choice for the the builders.....they can go and build something else! 
Seriously though, have you thought of what 12 meters [40 feet] might cost you, what the shipping cost will be, what's the chance of those long slender rails being damaged in transit, what will you fix them to, with screws at what intervals, and is that "precision" really necessary when cutting unstable wood or plastic? Have you ever picked up a 4m [12 ft] long top brand name linear bearing in the middle and seen how the $1000 ends droop by 6mm [1/4"]? Have you tightened a heavy linear bearing to a bed with a bit of dirt under it and seen how the rail bends? Okay, I am going too far now....
I also hate splitting long items, but I bit the bullet and got over it. |
DocTanner
Registered
Username: Doctanner
Post Number: 42
Registered: 11-2006
| | Posted on Wednesday, March 07, 2007 - 11:07 pm: |
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Bugmenot,
I only took a couple pics of the whole build, none of the rails. Will try to get a sketch of what I did.
Gerald's tablesaw method would have been my first choice, but I have a brand new tablesaw that I wouldn't let myself use.
My hobby can make money. My Mechmate has already paid for 1/2 of itself, so it must be close enough.
DocTanner |
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