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Weigh Mill Head

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  • Paul Alciatore
    replied
    Yea, I get this. It will probably work. I just have to find the manual crank. And dust off an old bathroom scale.



    Originally posted by Baz View Post
    I think there will be some backlash in the downfeed screw so as you lower the head the handle will have a little loose point as you go from tension to compression. If it is difficult to feel then, more laboriously, record weight against rotation of handle in say 1/4 rotation steps and plot. You will see the discontinuity in the graph.
    I'm assuming old fashioned spring based scales that have some movement, not a load cell based digital thing.

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  • velocette
    replied
    Hi Paul much better understanding now that I have read up a much fuller description of a Rong Fu 45 mill drill that has a sepperate advance on the quill for drilling and not sliding on the Gibs. Baz got it right for weighing the head.

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  • Paul Alciatore
    replied
    Does that assume that the tie down bolts will be loose while you are working? I always tighten them before working. And on this Grizzly version of the RF45 mill, with the motorized vertical head movement, you have to loosen them by about four turns to activate the switches to allow the motor movement. So there is no just "keeping the tension on the gibs at a slightly tight value". I would have to adjust it every time I move the head. I guess I could defeat the switches, but I hesitate on that.

    With the tie downs tight, I do not see any problems with any operations. Either now with the full head weight on the dovetail or with less or even zero percentage of that weight there. Locked down is locked down. No movement allowed. And that is the best condition for actual operation.

    Besides, if the gibs are not locked down, then the head will be at a front-back angle. And we go to so much trouble to tram it from side to side. Just getting into more problems, it seems to me.



    Originally posted by velocette View Post
    Hi
    Equal to the weight of the head will give problems with any backlash when drilling. JCByrd24 suggests 75% of the weight of the head will be fine to lessen the loading on gibs etc until the downward force on the cutter exceeds the remaining weight of the cutting head then backlash is a problem. With a counterweight of plus 25% of the weight of the head will be fine until a cutter drags itself though the work and takes out the dreaded backlash. Keep the Gibs fairly tight will help increase the effect of the counterweight.

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  • Baz
    replied
    Originally posted by Paul Alciatore View Post
    So, will I be able to tell when a scale or the counterbalance weights themselves take up the slack. I seems that I could wind up going the other way and have excessive lifting force on it.
    I think there will be some backlash in the downfeed screw so as you lower the head the handle will have a little loose point as you go from tension to compression. If it is difficult to feel then, more laboriously, record weight against rotation of handle in say 1/4 rotation steps and plot. You will see the discontinuity in the graph.
    I'm assuming old fashioned spring based scales that have some movement, not a load cell based digital thing.

    Leave a comment:


  • velocette
    replied
    Hi
    Equal to the weight of the head will give problems with any backlash when drilling. JCByrd24 suggests 75% of the weight of the head will be fine to lessen the loading on gibs etc until the downward force on the cutter exceeds the remaining weight of the cutting head then backlash is a problem. With a counterweight of plus 25% of the weight of the head will be fine until a cutter drags itself though the work and takes out the dreaded backlash. Keep the Gibs fairly tight will help increase the effect of the counterweight.

    Leave a comment:


  • JCByrd24
    replied
    The head of my PM-30 is around 60lbs, yours will be 2-3x that I'd say being gear driven and just more robust in general. For what you need to do I wouldn't worry about getting it too accurate. I'd guess you don't want to equal the weight of the head with the counterweight, you want to be like 75% so the head isn't floating on the lead screw. I'd plan on 100lbs and call it a day. More importantly you want to attached the cables to the head in the correct spot, which is near the center of gravity of the head, so it actually relieves the torque on the dovetails. My machine has an air piston in the column which aids in lifting but does nothing to counteract the cantilevered load. Luckily my head isn't too heavy. I actually dislike the air piston. It aids in lifting but when the head is low it actually fights lowering. Next time I have the head off I'm going to remove it completely. I think you're on the right track with a simple cable system.

    Edit: Found a couple references online to the RF45 head weighing around 200lbs.
    Last edited by JCByrd24; 05-16-2019, 09:16 AM.

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  • Paul Alciatore
    replied
    OK, I guess I should have mentioned that the head adjustment is motorized: it's a Grizzly G0484. It does have a hand crank, but there is going to be the drag of the motor of clutch or whatever. So, will I be able to tell when a scale or the counterbalance weights themselves take up the slack. I seems that I could wind up going the other way and have excessive lifting force on it.

    I am thinking about a counterweight system with pulleys. That way the weight of the head would be balanced no matter what position it is in. Besides, no air or hydraulic fluid leaks. I am debating as to weather to mount the pulleys on the ceiling or on a frame attached to the rear of the mill or it's table. This idea is still in the initial stages. But I do believe it is a good idea.

    I kind of want to know at least the approximate weight so I can get the proper pulleys and build the framework strong enough.
    Last edited by Paul Alciatore; 05-16-2019, 12:45 AM.

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  • A.K. Boomer
    replied
    put a jack on a scale - minus the weight of the jack when an equilibrium is met.

    Baz just beat me to it but i like his method better anyways

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  • Baz
    replied
    Originally posted by Paul Alciatore View Post
    My question is how can I find the weight of the head without taking it off the dovetails?
    Place bathroom scales on table, packed up as necessary, lower head onto it with very slack gib so you can see/feel how it balances. Raise head, turn scales round so you can see the bl***y display, try again.

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  • MikeL46
    replied
    You could hang a counterweight (50-100#) off the back and measure the movement when you loosen the clamps. Shoot for no movement and call it a day.

    Mike

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  • Bob La Londe
    replied
    Large air reservoir, air cylinder, adjust until you like it?

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  • Paul Alciatore
    started a topic Weigh Mill Head

    Weigh Mill Head

    I have a dovetail style mill,drill. The head hangs off the vertical column when the lockdown screws are loosened to move the head. This has several problems, including uneven wear on the dovetail ways and difficulty getting those lockdown bolts properly retightened. I am thinking about putting a counter weight on the head.

    My question is how can I find the weight of the head without taking it off the dovetails?
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