Author Topic: The "Mach4" 3D Laser Build  (Read 15912 times)

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Offline RICH

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« Reply #20 on: November 14, 2014, 07:14:35 AM »
Quote
Thou I'm not sure how id test for what the limit might now be.
Scissor lifting tables are not linear in there ability to lift weight or position.
the graph shows some rough plotted points I'd created.


Graig,
The ability to lift with the table would be motor torque limited.
To get a close approx just put a weight on the table say 10# and see how much torque is required
( hopefully you have inch # torque wrench...) at 1 or two inch intervals. Do the same for say 20#, what ever #, or max wieght
you intend on putting on the table and graph.

Dosen;t matter how they rate the tables, I am sure you will not shear the pins or break the screw. Once the table cross legs
create a 45 deg angle uplift force will increase.


RICH
« Last Edit: November 30, 2014, 09:58:26 AM by Ya-Nvr-No »

Offline RICH

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« Reply #21 on: November 14, 2014, 07:41:46 AM »
Graig,
None of the sizing software I have has a scissor jack configuration system.
But you can have a look at the following and have some quick and dirty data for your use.

http://www.engineersedge.com/calculators/scissor-lift-bottom-loaded.htm

BTW, if you did a verical lift instead of the scissor you would of had linear movement and and constant loading.
Use counter weighted assist and could have used a wimpy motor.........

RICH
« Last Edit: November 30, 2014, 09:58:39 AM by Ya-Nvr-No »

Offline Ya-Nvr-No

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« Reply #22 on: November 14, 2014, 07:54:11 AM »
Thanks Tweak, Your laser project inspired me to have one of my own.

Rich, not worried about breaking the table but was wondering how the table was rated at 50 pounds as advertized.

And i guess I'm a little confused how I'd use a torque wrench  ???

Id thought a hanging scale at interval in positions along the travel. (so it would pull at itself)
As there has to be different values at different positions.
Getting it off bottom seems to be the low weight lifting limit and at the last is the max weight lifting limit.
So do they rate it mid stroke or at that 45 degree angle?

as a side note the pillow blocks were provided by Rkjohn (Thank You)
http://www.machsupport.com/forum/index.php/topic,25244.msg178399.html#msg178399

the short pieces of 5/16 shafting is from the scrap bin of a local machine shop running swiss automatics, they are the ends from the bar feeders.

I purchased from Russ (Overloaded) the Aluminum extrusion material.

The Aluminum blocks are from the local scrap dealer that sells me whatever I find at current market rate.

had to purchase the 3/8" Drill rod and still waiting for a 12mm Drill rod that the USPS lost the first shipment (so the hole you see is in need of the additional guide rod)

Most all else in hardware was ebay purchases.

Opps, Missed the Y axis rails, they were from a palletizer table that was decommissioned and I had on hand for several years. I  just cut off what I needed for the framing material I had to work with.
« Last Edit: November 30, 2014, 11:46:55 AM by Ya-Nvr-No »

Offline RICH

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« Reply #23 on: November 14, 2014, 08:41:39 AM »
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And i guess I'm a little confused how I'd use a torque wrench

You turn the screw with a torque wrench. I am lucky in that I have one that has dial indication which when observed will show
the torque that was required ie; just to start turning the screw, how much torque was applied to continue moving the axis.
I use it to adjust bearing preload ie; it indicates the difference in torque required to just move the axis , so if i adjust the preload
to remove / reduce backlash  I know how much of available motor torque was used since you want you want minimize it.

If you were to put say a 50 # weight on the table and see what setting the torque wrench click's  at you have the torque required
to lift that wieght which will include all the friction factors or binding in the table which is better than tryng to add assumptions
if calculated. Try the table when all the way down, at 45 deg angle ( probably half travel ) and just about at the full travel.

You could also use the torque wrench by reducing it's setting to see where the motor will not stall / skip.

All this can be done quickly,but, i will add that you should have confidence in the wrench settings.

SAFETY:
You wouldn't try to measure the torque of you car engine this way to see what force at the handle was required so common sense
is required if you have really high torque motors on your machine.

Hey, Hey I still remmeber our Hillman Minx car ;D with column mounted 4 speed reverse pattern  ::), that had a hand cranck which you could use until you could afford a new battery.
Crank handle could rip your arm off in a heart beat if not done correctly. ???

RICH
« Last Edit: November 30, 2014, 09:59:01 AM by Ya-Nvr-No »

Offline Ya-Nvr-No

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« Reply #24 on: November 14, 2014, 09:44:53 AM »
Thanks Rich for taking the time to explain. I did have to look up the Hillman Minx car, Cute  ;D

Seeing that screw mapping has not been implemented as of yet:
I did some spreadsheet work on creating a formula to calculate the logarithmic scale for the scissor lift

the red line is the calculated log line

Why I dont throw books away  ;) and the hutch I'd refinished was the storage source for the reference.

Craig  ::)
« Last Edit: November 30, 2014, 09:59:10 AM by Ya-Nvr-No »

Offline Ya-Nvr-No

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« Reply #25 on: November 14, 2014, 11:47:37 AM »
Just did a crude test using the hanging scale, doing the best I could without stressing to failure I got the following.
The pmdx board faulted out on the lower three heights but I never pushed it beyond the third test height as I did not want to create mechanical failure.
the inch value is the overall height of the lift table, used as a reference value.

@bottom 5-1/2" pmdx stopped at 25#
6-1/2" 55#
9-1/4" 110#
11-1/4" 140# I stopped
11-3/8" 180#
« Last Edit: November 30, 2014, 09:59:20 AM by Ya-Nvr-No »

Offline RICH

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« Reply #26 on: November 14, 2014, 08:29:34 PM »
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Why I dont throw books away


In my case I sometimes have a "figment of imagination" that i may go back into doing engineering work. :D
Heck, the ceiling hasn't caved in yet from the stored books in the attic...........sometimes one should forget and move on!
Women don't understand this, but, what would you expect form someone who came from Venus! ??? :D ;)

RICH
« Last Edit: November 30, 2014, 09:59:30 AM by Ya-Nvr-No »

Offline Ya-Nvr-No

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« Reply #27 on: November 14, 2014, 09:31:58 PM »
No wonder she lets you have the basement as your man cave,  ;D
« Last Edit: November 30, 2014, 09:59:44 AM by Ya-Nvr-No »

Offline Ya-Nvr-No

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« Reply #28 on: November 28, 2014, 06:28:54 PM »
Few more photos, also added roller bearings to the focus head for alignment. Sure works smooth now.
« Last Edit: November 30, 2014, 09:59:53 AM by Ya-Nvr-No »

Offline Ya-Nvr-No

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« Reply #29 on: November 29, 2014, 06:39:23 PM »
Cabinet about ready to mount.
« Last Edit: November 30, 2014, 10:00:05 AM by Ya-Nvr-No »