Page 1 of 2 12 LastLast
Results 1 to 10 of 12

Thread: Weigh Mill Head

  1. #1
    Join Date
    May 2002
    Location
    SE Texas
    Posts
    12,204

    Default 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?
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

  2. #2
    Join Date
    Jan 2014
    Location
    In the desert
    Posts
    1,273

    Default

    Large air reservoir, air cylinder, adjust until you like it?
    *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

  3. #3
    Join Date
    Aug 2014
    Location
    San Jose, CA:Vancouver, WA
    Posts
    310

    Default

    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

  4. #4
    Join Date
    May 2013
    Location
    UK, near London
    Posts
    1,207

    Default

    Quote 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.

  5. #5
    Join Date
    May 2006
    Posts
    14,841

    Default

    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

  6. #6
    Join Date
    May 2002
    Location
    SE Texas
    Posts
    12,204

    Default

    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 at 12:45 AM.
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

  7. #7
    Join Date
    Jan 2017
    Posts
    165

    Default

    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 at 09:16 AM.

  8. #8
    Join Date
    Oct 2011
    Location
    Hawkes Bay New Zealand
    Posts
    229

    Default

    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.

  9. #9
    Join Date
    May 2013
    Location
    UK, near London
    Posts
    1,207

    Default

    Quote 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.

  10. #10
    Join Date
    May 2002
    Location
    SE Texas
    Posts
    12,204

    Default

    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.



    Quote 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.
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •