head out of tram on BMC20

[JWC]

When I set up the machine I went by the Hurco manual that said to use a precision level on the table. I read in another post for Fadals that the the way covers should be removed, ways cleaned and to use them for the leveling process. I then saw on another board to level a vmc by leveling a surface plate on the table then adjust the leveling bolts til it trammed within .001 or better regardless of the way or table level. Any other suggestions?

[JWC]

bump

[Caprirs]

Although I'm not familiar with the Hurcos, this is the method I've used.

- Start with only the four outermost corner screwjacks touching the floor. All others should be up off their pads. Using a machinists bubble level on the table, get the machine to within .005" per foot. The idea of being level to earth is so the column is as straight up and down as possible and not leaning in any direction. Rotate the level 90 degrees to check front-to-back and also left-to-right.

- When the machine is level to earth, place an indicator in the spindle with the tip on the machine's table. The more precision the indicator, the more accurately you can tram the machine. The larger the circle the indicator can sweep as it rotates, the more accurately you can tram the machine. I like to use a .0001" indicator and sweep a ~6" circle when possible.

- Using the middle screwjacks only (do not change the four corners unless absolutely necessary), bring them down to just barely touch their pads. Sweep the indicator around the table and note where the high and low spots are. What you are going to do is "flex" the base of the machine causing the column to move up/down/left/right using a combination of the inner screwjacks. Despite the heft of the machine's base, it will flex under the weight of the rest of the machine sitting atop it. This takes some trial and error and it can help to have two people so one guy sweeps, while the other wrenches the screwjacks.

- A little turn on the screwjack can have a measurable effect on the indicator. For example, a quarter turn on the screw might give .001" indicator change.

See the attached dxf for an exaggerated illustration of how the flexing of the machine base affects the tram of the head.

[JWC]

Thanks for the reply Caprirs. My BMC20 only has 4 jackscrews but I think I can get the same result from them. My next goal is to tighten the gibs on the z axis. I see locking screws along the right side of the head and screws on the backside of the head along the ways. I can't find any instruction for tightening or aligning these except for voltage/amperage specs.

[JWC]

I put a small granite surface plate on the table and leveled it in x-y with 3 machinist jacks. I then put a ground angle plate on it(checking it in 4 directions to make sure it's 90 deg). I adjusted the floor mounts to bring the z column in. It's no where near the level it was but the z axis is perpendicular to the x-y plane. The spindle tram is way off and the cause seems to be the head is somewhat loose and the gibs need to be tightened. I can move the head considerably just by pushing on it. I see set screws on the right side as I face the machine and screws behind the ways on the head on both right and left sides. What is the proper way of tightening the head?

[Caprirs]

What kind of ways does the machine have? Box? Dovetail? Linear?

The voltage/amperage specs are so you can measure the friction when the axis moves. My machines have Mitsubishi controls where I can see the current load rate on each axis.

With most box and dovetail ways, there is one adjustment screw at each end of the gib. Initial gib adjusment is usually done using an indicator. As the mechanical slack is taken out of the axis by snugging the gib, the voltage/amperage of the servo becomes more useful for checking for an overtightened gib.

[JWC]

Originally Posted by Caprirs What kind of ways does the machine have? Box? Dovetail? Linear? The voltage/amperage specs are so you can measure the friction when the axis moves. My machines have Mitsubishi controls where I can see the current load rate on each axis. With most box and dovetail ways, there is one adjustment screw at each end of the gib. Initial gib adjusment is usually done using an indicator. As the mechanical slack is taken out of the axis by snugging the gib, the voltage/amperage of the servo becomes more useful for checking for an overtightened gib.

They are box ways. I have the spec sheets for the current load but the gib adjusting is pretty vague. Would it be under the cover just above the way like a dovetails way on my km3p? There are so many set screws along the head.

[Caprirs]

Box ways are hungry for way lube but allow you to take heavy cuts.

I have no idea what the set screws are. That would be a question to ask Hurco. They may have a procedure they could fax to you for performing these adjustments.

Yes, the adjustment screws would be similar to the ones on a Bridgeport manual mill. When I do gib adjustments on a VMC with box or dovetail ways, I start by placing an indicator against the axis I'm adjusting. For example, if I'm adjusting the Z axis gib, I place the indicator in the spindle with the tip resting against the side of a vise (or other flat machined rigid surface. I stand to the left/right of the head and push it in the X direction. Then move to the other side and push in the opposite direction. When pushing on the axis, I get deflection than more .0004" while I'm leaning on it but it springs back when I stop pushing. Ultimately, the gib cannot be tightened to eliminate all the slack because that would not allow the axis to move. I have found that it is tough to get below .0004" without causing the axis to bind up.

Further tightening must be done using the electrical specs because the axis is on the verge of binding. The ways function by floating on that thin layer of way lube. If the gib is adjusted too tightly, the way lube is squeezed out and metal-to-metal contact occurs.