Quill and head problems?

[wildcat]

Sorry, I am going to be a little long-winded here but I really would like someone's input on what I am seeing. I have sent the following information to Aaron at IH but I had hope that others might add their opinion. The main problem is that I am having problems getting reliable cuts in a reasonable fashion. E.g. I move to cut a couple of thous and find I had cut 7 or so. It seems that a lot of this error comes from the deflection of the quill and head. What I mean by "reasonable" is that I think I should be able to move the quill either by loosening the quill lock, moving, and tightening or moving the quill with the lock snug without undue force and maintain position. However, it seems to maintain position I must keep the quill really tight and/or move in the Z by raising the head. However, the gib needs to be so tight in the head that it sticks and falls while moving down making it dangerous to work pieces. Please read on to see what I did and what I saw.

Following the instructions for tramming on IH's website I mounted an 8" ground square on the table and place the point of a dial indicator against the blade. I ran the head up and down indicating the error of the head's movement in the X and Y dimensions. I also did the same with the quill and found a lot of runout in the quill unless I tightened the quill up to nearly the point that it cannot be moved with the microdial along. With my hands alone I can deflect the quill .006 in some cases. I can't imagine how much an endmill would deflect the quill. As it is now unless the quill is tightened before indicating the edge of a piece and left tight there is a lot of error present. (I included the raw measurements below.) The head appears to be fairly square with the table. With some squaring of the head I can improve the situation some as seen in the tight column. I guess what I am concerned most about is that I need to keep the quill so tight to maintain position and how easily the quill and head deflect with just hand pressure.

Also I have a problem with the head movement. In order to maintain position of the head I had to seriously tighten the gib. In fact I had to shorten the gib screw in order to have the travel necessary before bottoming the screw out in the threads. After doing this the head has less deflection (the numbers here measured after doing this), the head was more square with the table, and tightening the gib locking screws did not deflect the head. However, the head sticks while moving up and down. It is not such a big deal that it sticks moving up - a little extra muscle is all it takes, but moving the head down is a little different. The head sticks but I am still cranking and then all of a sudden the head drops what seems like a lot. I was able to take some of this out by inserting about 3/8" of spacers under the cap holding the z-axis on top of the column but there is still some head falling happening. I don't know if more spacers will help. I added spacers after noticing that when change directions cranking the Z-axis handle would move the entire head leadscrew up. The bevel gear on the leadscrew did no move and the key kept the screw and gear connected. The head would ultimately fall the distance the lead screw was able to move in the bevel gear. I have lapped the Z-axis.

To summarize my questions:

1) Is it reasonable to be able to deflect the head .005 or the quill with a person's hands alone?

2) Is it reasonable to have to tighten the quill to maintain position so much that it is barely movable?

3) What can be done to keep the head tight but not fall while moving down as it does now? Does this mill need to have the Z-axis modification that IH shows on their web site where the head is more rigidly attached to the Z-axis nut? Is a ballscrew needed?

Raw data:

The measurements read off the indicator while moving it along the square with various tension on the quill and the deflection at the top and bottom of the 4.5" travel created by pushing with only my hand:

Loose Mild Tight
Y-axis Travel .005 .003 .002
Deflec Bot .006 .001 .0005
Deflac Top .006 .001 .0005

X-axis Travel .007 .004 .001
Deflec Bot .004 .003 .0005
Deflec Top .002 .002 .001

An additional .005 deflection in the X comes from simply pressing on the head, which drops to .003 after seriously tightening the screws and this is after tightening the gibs.

7.5" travel of the head has runout of .001 in the X-axis and .000 in the Y-axis.

[wildcat]

Hmm... why is after posting I always seem to find a thread that covers my question? It looks like my numbers are right in line with what others have seen regarding the quill quality. Guess I will lock the quill down and work on removing the sticky points in the column. This weekend I will pull the head off and see if it needs the modification that Aaron has on his website and rig up a counter balance system. I plan to go cheap and use pulleys and weights. Do you think this will cleanup the sticking and play in the movement of the head?

Thanks.

[BobWarfield]

I'm doing fine with mine if I just lock the quill. I did measure a lot of slop in the quill. My Z-Axis on the column doesn't stick. I have lubed it carefully and adjusted the gibbs. I understand some others have seen sticking problems. I also know Aaron's modification is HIGHLY recommended.

I can't imagine why counterweights wouldn't be an awesome idea in any event. Do take care where you attach them as half the battle is that the head cantilevers. You want to not only relieve the weight, but also the cantilevering.

Interestingly, Aaron on his site suggests that the gibbs on these machines be very seldom adjusted (4 times a year with the seasons), that they be adjusted as tight as can be and still get smooth travel, and that they never be locked, as locking will change your position, especially on the Z-axis.

I had been locking mine to reduce rigidity, but will try it Aaron's way when I get back to playing with the mill again soon.

Best,

BW

[wildcat]

Bob, I assume you meant you were locking your gibs to INCREASE regidity

Unless I really tightened the gibs screw there was a lot of movement in the head (at least .005 in one axis) when I locked the gib. Surely if locking the gib is moving the head then maching forces would as well.

This weekend I plan to pull the head off and get a better idea of what is actually going on. The current idea is, after checking if the head modification would help and checking the acme screw in general, to hang some weight off the bottom of the head slide. Since I am using my machine in a manual mode I am not worried about motors driving the extra weight. Since I am using the acme screws there is quite a bit of backlash and since I had to tighten the gib down pretty snug to take up the head deflection the head sticks in places. It would seem that the addition of maybe 50 lbs hung off the bottom of the slide would help to overcome the sticking and keep the head firmly down against the acme screw and lock the gib when I want the Z to stay put. It would seem that unless the jib is locked that without a ballscrew and motor keeping it in place the head could wander down. Anyway, if the extra weight does not do the trick then on to trying a counterbalancing system.

Regarding the quill - I going to leave it up and locked down snug - my HF drill press is actually better. For z-axis measurement I guess I will mount a caliper on the column. I don't want to spend the cash on a DRO for this mill until I have more experience with it to know if it's justified.

I can understand now why some call the import mill/drills "mill kits" I am sure it will be nice after all the kinks are worked out however.

[Cruiser]

hanging the weight from the bottom of your z slide will make it worse, hang the weight behind the column using cables and pullys up and over. mounts for cables will have to be to hollow portion of box not entering oil chamber, and as far to front as possible, and definately get the z saddle modification done by aaron. better concider at least a little bit of lapping too to insure a smooth slide.

[BobWarfield]

Originally Posted by wildcat Bob, I assume you meant you were locking your gibs to INCREASE regidity

I guess you could view it as increasing rigidity, and that was why I started out doing it. In the end, I realized it was going to flop around to much to accurately align to the parts until I locked. So I run it down to depth, lock it, remeasure Z, relock, yada, yada, until it is in the right place. It works, and you get used to how to tickle it into position pretty quickly. A Z-Axis DRO is hugely useful for this. I made up a real cheap set of DRO's and have found it well worth it:

http://www.thewarfields.com/MTMillDRO.htm

Cruiser is right. You need to counterweight and reduce the weight, not add more to it. You also need to use pulleys or offsets if using gas struts so you take the weight off at the center of mass of the head (center along spindle axis is probably close enough, even if done at top or bottom). You want to really counteract that cantilevering. 275lbs is a lot of lead hanging out there, so I am more a fan of the gas spring approach:



Thomas Powell worked out that design, details on his site:

http://imageevent.com/tppjr/rf45dove...scounterweight

I'd be real tempted to try to attach the cables a little more towards the front of the mill myself. A clever man might even hide some of this gimmicry inside the voluminous column--gas springs are small.

Another fella on the 'Zone just stuck a gas spring on either side and attached one end to top of column and the other to bottom side of head. That was real clean, and worked well. It's one disadvantage is that because the gas springs are angled, their force changes as you move the head up and down. He says its not a problem.

Best,

BW

[wildcat]

Regarding adding weight - I knew I would hear from someone about doing that What seems to happen now is once the backlask of the screw (and related slop) was been taken up the screw gives the head a little push and down the head comes. It would seem that a slight pull at the bottom of the slide, so close to the column, would be enough to keep the head down against the screw and not add to the cantilevering but instead overcome the friction. This will not work? Lapping has already been done though perhaps not enough? I can't really say that lapping helped much more than apparences and I think others have mentioned that biggest benefits of lapping are to CNC conversions while mine is manual.

Bob, I was looking at exactly those scales on eBay and I am glad that you show how to mount them. That helps a lot to know they mount welll. Also, I have seen the counterbalance pictures you referred to. The gas struts on the side of the head is a nice looking system but I was surprised over the expensive of gas struts. I will give it some more thought.

Thanks

[BobWarfield]

I think that the little push, followed by slip, happens because of all that cantilevered weight. Think about how it tries to cock the head in the slideways. Aaron actually uses an even longer slideway so it has more leverage against that in his latest incarnation. If you add weight, you are just causing the forces to be even less equally distributed over the slide.

You want to adjust the gibs carefully so there is no room for "cocking" (i.e. make it hard for the head to tilt down in front), generously lube everything, and potentially counterweight to further reduce the cantilevering.

Mine never slips in little jumps, and after I put way lube and lubed the screws, I noticed if I didn't keep the gibs tight, it would slowly and smoothly slide down with vibration. So, from this, I know smooth travels are possible, at least in one case! LOL

Call Aaron too. I've seen other reports of this from time to time and given similar advice. He almost certainly knows even more tricks.

Best,

BW

[QSIMDO]

I don't think I'm telling tales out of school to say that I very recently had a short conversation with Aaron re the head slide mod and he advised against it if the machine was to stay manual.

The reasoning is that if you solidly mount that area and there is any slop elsewhere at all with the Acme lead screw you'll bind up. CNC folk are changing over to ball screws so alignment isn't a problem, therefore the head needs to be as rigid as possible.

Wildcat, I'm having the same symptoms as you and, nearly as we speak, I'm lapping the column as step one to the grip/slip problem.

However, if we study the design closely we must arrive at the undeniable conclusion.... we are screwed! (Shoulda bought the Bridgeport )

I say this with no rancor at all. It's just the facts.

But part of the fun is trying to think through these situations
For now I'm just trying to get it smooth (even if the head is a bear to move with the gib tightened) and then work within the limits and capabilities of the machine.
(Yet all the while plotting and pondering a fix and praying the plagirists prayer that someone beats me to it! )

More ideas then!!

[wildcat]

Bob, Cruiser, and QSIMDO, thanks for the suggestions and warnings - I will certainly pay attention. When I got home tonight Aaron had left a message and hopefully we will get in touch tomorrow. If I remember, I will ask him about perhaps using his mechanicals to convert the Z-axis to motor drive if that would do the trick. Well, got to go open up some boxes of goodies from Enco.

[wildcat]

Anyone have any suggestions for a gas strut that has a longer travel than 12"? This picutre that Bob posted looks like a really nice solution (compared with free weight) but limiting counterbalanced travel to 12" is the not great especially when yo consider 4-5" of that travel is taken up if using a vise or rotary table but still want to be able to come down to the table to use fixtures. I assume that a person could simply tie two struts together end to end. I would guess the two 150lbs struts together is still a 150lbs but just twice as long.

[Cruiser]

If ya really want to use it then i'd suggest mounting it to the gear box persay normally and build a bracket with multiple mount locations so that you can set it to were your work is going to be.........ps ... Don't mount it the same as the pic above, mount it more to front in the cavity area behind spindle, this will allow you to tighten gibs a bit more and reduce some of the cantilevering, still allowing the head to be supported with your strut ! OH YA, I think i've finally figured out what Aaron meant by "pretty darned tight" pertaining to the Z saddle gib, mine is now tight nuf that i can't get a .003 feeler to catch gap at the top, and it travels full steam with no complaining at all from drive system of Aaron's servo config. If ya can swing the change then go for the gusto and go full cnc, The IH cnc system is strong.