Need Help!- Mill / Drill Table "Twisting"...?

[ShopMonkey]

Hi Guys,

This is my first post and I'd like to start by saying hi... and thanks for having me in...

I've come seeking assistance with a problem that I'm having with my BusyBee CT129N Mill / Drill... I'll do my best to explain the issue but seeing as I'm somewhat new to owing this type of machine, please don't hesitate to ask me to try and do a better job explaining what I mean, as I'm not certain how well I will be able to explain what the problem is...

The best way I can describe what I think is happening is that the table on the mill is "twisting" as it moves through its range of travel, and here's my reason for thinking so...

I have a Starret 6" machinists level which is graduated in .005" / foot increments. With the table positioned all the way to the right on the X axis (longitudinal axis), I place the machinists level on the far right hand end of the table oriented on the Y axis (vertical axis, across the T slots, perpendicular to the T slots) and it indicates level. As I run the table to the left the level begins to indicate that the front edge of the table is "rising". This "rise" begins at approximately 1.5" before the center of the table (at the 1.5" graduation on the strip on the front edge of the table, the 1.5" graduation on the left hand side of the "0" mark). Between the 1.5" graduation on the left hand side of the "0" and the 1.5" graduation on the right hand side of the "0" the level moves almost 3 graduations (approximately .013" / foot) and then remains there until the table reaches the far left stop. So the difference in the level reading (with the level sitting on the right hand end of the table) between the far right and far left hand stops on the table is almost .013" / foot. My feeling is that this isn't a good thing.

The same thing happens regardless of where along the table I place the level (with the level oriented on the Y axis, the vertical axis, perpendicular to the T slots).

Additionally, with the table in any given position along its longitudinal travel on the X axis with the level oriented perpendicular to the T slots, as I move the table forward along the Y axis (toward the column) the level indicates that the back edge of the table is "rising" by approximately 2 graduations on the level (approximately .010" / foot) in the 7" of Y axis travel.

In attempting to understand what is happening, I have adjusted both the X and Y gibbs almost to the point of not being able to move the table, and while this affects the initial reading on the level, the relative "twisting" of the table as indicated by the level during table travel remains as described above.

I'm sorry that my description of this problem is so cumbersome but I wanted to try and make the details as clear as possible.

If someone could please help me understand what might be going on with this it would be very, very much appreciated...!

Thank you all in advance for your assistance...!!

Dave.

[NC Cams]

Try jsut baerly tightneing things so they don't move. You may be VERY sruprised.

Small machines are ground unassssembled and then assembled. Due to the lack of mass, they can easitly move around when you starrt to tighten things to set the postion.

If the machine is moving around when you tighten things up, it may simply be something you'll have to live with. Fixing in would involve finding a way to prestress the table and blanchard grind it while prestessed - probably might cost you more to fix than the cost of the machine new.

SOrry to say that some of the small mill/drills are more drill press than milling machine. It is hard to get/expect Bridgeport mill accuracies out of a bench top machine.

By the way, we level our cam grinder with 0.0005" per foot levels and we get it there and it stays so. It can be done with enough mass in the machine.

Heck, you can even see table droop in our Bridgeport mill when you run the table from one end of X to the other. Tram spindle with table centered, keep 0.0005"/ft level away from it and live with the rest. THe BPT simply can hold up its own weight with respect to gravity.

[ShopMonkey]

After much searching I found this post in response to a member that was having the same issue... the method of discovery was different (he used a DTI rather than a level) but the symptoms are the same... I linked the thread at the bottom...

I'm gonna' give Tigers suggestion a try and see where that gets me. When he says "lapping" it's a bit of a misnomer... really what he's suggesting is a "dedicated effort brake-in" (to coin a phrase)...

Originally Posted by WhiteTiger I suspect you are looking at surface finish and adjustment issues. These budget mills generally have fairly accurate ways, but the surface finish is lacking, which makes them move stiff and irregularly when properly adjusted. Result: most users tend to adjust them for initial ease of movement which introduces functional (but not felt) slop in the fit. The horizontal bed surfaces are usually fairly good, but the dovetail rail surfaces can be rough as a cob and since those are where the gibs reference to and ride against, the movement is stiff as a board during break in unless the adjustments are backed off for smooth motion. The safest, easiest cure I know of for this is to strip the machine down, and oil up the ways with a good cutting oil (I like Marvel Mystery Oil, available at any auto parts) then reassemble just the saddle on the Y axis ways, adjust till you can just push it with effort, and spend a few minutes shoving it back and forth full stroke on it's ways. Then spend about 1/4 that amount of time short stroking just the ends of the ways, taking them a bit out of engagement if possible. When it gets easy to move, disassemble, wipe everything down to clean off the iron particles you probably will note turning the cutting oil greyish, then repeat at least one more time. Once the Y ways are broken in and final cleaned, reassemble them dry and lock the gib down solid, then repeat the whole thing for the X axis. It's important to lock down the Y axis, as rocking in it can introduce force errors in your self lapping of the X ways and make them come out irregular in extreme cases. When working the X ways, be sure to hold and support the free hanging end of the table when you are short stroking the ends of the table ways (which has to be done to offset the wear distribution, since the center of the table ways gets double the wear with each full travel stroke. It's tedious, but it pays big dividends. Took me about an hour and a half all together to break in all the ways on my old bench mill, not counting the scraping of the saddle X axis dovetail surfaces. Once you have all the surface roughness knocked off the mating surfaces, you can adjust the gibs correctly and not have them compress the high spots of their mating surfaces and give you deflection under load. Tiger

http://www.cnczone.com/forums/showthread.php?t=17125

[ClintonH]

Hey Dave, I'm the guy you met over at Busy Bee. If your going to go through all that trouble you mine as well do it right and lap it if when you get it apart you think it needs it. Here's a link to how to do it proper, just scroll down to the end of the page and work your way up. For the different grits you can use valve lapping compound, should be able to get that form Princess auto or Greggs Dis. And the link I was going to send you. Hope you figure it out.

Clinton

[ShopMonkey]

Originally Posted by ClintonH Hey Dave, I'm the guy you met over at Busy Bee. If your going to go through all that trouble you mine as well do it right and lap it if when you get it apart you think it needs it. Here's a link to how to do it proper, just scroll down to the end of the page and work your way up. For the different grits you can use valve lapping compound, should be able to get that form Princess auto or Greggs Dis. And the link I was going to send you. Hope you figure it out. Clinton

Hi Clinton...

Thanks very much for the links, I appreciate it and I'll check them out. Having said that, I've been reading a very detailed thread here that suggests that lapping might not be the best way to go - which is why I like Tiger's suggested process, at least to start. There are some very learned dudes in the thread that I'll post below that suggest that lapping may in fact do more harm than good...

http://www.cnczone.com/forums/showthread.php?t=11874

The more I read about it and the more I play with the mill, the more Tiger's description of the issue makes sense to me. The gibs on my mill are rough as rough can be and from what I understand, once I can get the mill to operate smoothly with the gibs properly adjusted (which at this point is impossible - when adjusted so that there's no play in the table, the table is locked solid) I'm hoping that I'll be on my way...

Thanks again for the info, I'll definitely check out the links and let you know which way I go, and how it all turns out.

Dave.