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  #1  
Old Sun 25 May 2008, 05:42
drieslaas
Just call me: Dries
 
Pretoria
South Africa
Spring tension adjustment - is it needed?

Hello people,

I have built a machine very similar in architechture to the Mechmate.
A possible suggestion is to bond the racks onto their supports with epoxy.

Very quick, it handles the loads with ease, is removable (with judicious use of a heatgun) and no drilling required.
Another advantage is that the joining of racks end-to-end becomes very simple.
Just bond them in the right position, using a short piece of offcut rack turned upside down and meshed with the two sections being joined to keep the pitch right.

The pinion does not even know about the joint.

On the subject of backlash between pinion and rack, I use exactly the same principle, only difference is a bottlescrew (turnbuckle) instead of a spring.
No problem so far, touch wood.

Regards,

Dries
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  #2  
Old Sun 25 May 2008, 09:52
dmoore
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Quote:
Originally Posted by drieslaas View Post
On the subject of backlash between pinion and rack, I use exactly the same principle, only difference is a bottlescrew (turnbuckle) instead of a spring.
Dries -

Do you use a turn buckle with a spring like this:


Or do you use just a turnbuckle?

The advantage on the MechMate with the use of properly tensioned springs is that if you hit a stop, the spring will allow the pinion to ride up and out of the rack - protecting the motor.
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  #3  
Old Sun 25 May 2008, 10:57
isladelobos
Just call me: Ros
 
Canary Islands
Spain
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This is more precise and easy to install, only need a hole in the plate engine



otro facil de construir.

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  #4  
Old Sun 25 May 2008, 14:14
dmoore
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Those are nice but I'm still not seeing an advantage over just $10 worth of springs for the entire MechMate. The springs work very well, are inexpensive, allow the pinions to pop out when they hit the stops and don't suffer from vibration and they also maintain zero backlash.

Thanks,
david
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  #5  
Old Sun 25 May 2008, 14:56
J.R. Hatcher
Just call me: J.R. #4
 
Wilmington, North Carolina
United States of America
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David, I've hit the stops darn hard on my machine but the pinions have never popped out because by that time the steppers have no power, the limit switch has already been tripped.
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  #6  
Old Sun 25 May 2008, 20:54
dmoore
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Quote:
Originally Posted by J.R. Hatcher View Post
David, I've hit the stops darn hard on my machine but the pinions have never popped out because by that time the steppers have no power, the limit switch has already been tripped.
For those, like Gerald, that don't run with limit switches - it's easy to misjudge and run into the stops at full power. Of course when that happens - something has to give and with 7.2:1 geared motors, its not them. So with the MechMate, the gears "ride up" out of the rack against the tension in the spring. So, I'd say it's a good idea to have a spring with "just enough" tension to remove the backlash and hold the motors onto the track but not any more.

It's a good design feature - much better than when the same thing happens on a screw based design - where either the coupler breaks or the nut strips out, both that require repair.

I agree with you - with limit sensors are the way to go, and with soft limits in Mach3, you should never hit anything even on accident.
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