PM833TV alignment question

[Dan Thompson]

I recently purchased a PM833TV mill and I think I have a problem with the alignment of the mill. I have measured the tram on the Y-axis and found that there is 0.0035" of column tilt (or head nod) if you prefer. This was measured across the entire width of the table. I would like to know what other owners of this model of mill have experienced. This amount of tilt seems excessive considering there is no easy way to adjust it out.

 

[ddillman]

If you do a search there is probably a solution here. I don't know about your machine but some machines you have to shim them.
also all machines need adjustments

 

[mksj]

Not uncommon to see (I also had some with my Optimum new square column mill), make sure that gibs on the head are locked and the Z axis gibs are adjusted properly. There are numerous posts on the topic, as well as YouTube videos.

Tramming my PM-833TV

All of my experience in the past was on full size Bridgeport mills. I'm discovering that these column bed type mills are a different animal as far as tramming goes. I've done some research but would like to hear from others the techniques they use. Here is what my gut and a little research...

www.hobby-machinist.com

Another PM-833TV thread!

It took a few hours but I got the backlash fixed, or at least better. I was originally measuring about 10 thou on the x axis and about 15 on y. After a lot of measuring and fiddling I found it was due to a combination of preload on the lead screw bearings and backlash in the brass split nuts...

www.hobby-machinist.com

 

[davidpbest]

Dan, make sure you check other alignments as well, especially that the quill and head travels are coplanar to each other, and the X and Y axis travels are perpendicular to each other. I posted a video on this earlier, you can find it here:

Most likely you will need to shim the column.

 

[Dan Thompson]

Hello David. I'm glad you chimed in. I was hoping I wouldn't have to shim the column but I suspect you are correct. I read some earlier posts you made last year regarding fitting gibs. Could you comment on the desired surface texture (or lack thereof) on the gibs. Tech support at PM stated that the gibs should have a surface finish similar to the ways so as to retain an oil film. I have only removed and examined the Z-axis gib at this point and it has a somewhat rougher texture than the ways. The gib also has a few thousands of bow as measured with feeler gauges and a surface plate. I don't know how I would correct this without affecting the taper of the gib. The Z-axis locking levers also have more of a spongy feel than either the X or Y axis locks but they have to counteract the force of gravity pulling on the head whereas the X and Y locks don't so would this be expected?

 

[davidpbest]

PM will probably disagree with me - they jumped into this discussion earlier: https://www.hobby-machinist.com/threads/pm-728v-t-table-stiction.102898/#post-993843

In contrast to other aspects of these Taiwanese machines, I find the gibs positively crude. My 1340GT and 935 both had gibs that looked like they were hand cut with an angle grinder. Quite a contrast to the gibs that came on my RF-45 from Rong Fu. I would expect that on something from mainland China, but . . .

I hesitate to mention this given you are in touch with PM and their comment on the thread mentioned above, but I found it possible to flatten the gibs just by selectively pounding on certain points with a hammer while the gib was on a piece of plywood. The spony-ness of your Z could well be related to the bend in the gib, and it's entirely possible that PM would say that's by design. The head hanging off the column front adds a big torsional load that doesn't exist on the XY table, and the bend in the gib could be intentional to give the head more "slop" to be easily moved up/down. Hard to know, but I found the same thing on the knee of my PM-935 - it would chatter moving down, and I found that flattening the gib and holding tighter tension with the locking levers helped that tremendously. Even with a counterweight system, the head-to-column fit would need to be a lot less sloppy for a successful CNC conversion - which is one of the target applications for the 833. If you haven't already, I suggest you watch the 4 videos here - useful background if nothing else:

Highest quality gibs will be scraped with a pattern that allows for oil retention. But that's a whole other kettle of fish.

I guess soon enough, you'll be making your own ZCI's for Felder equipment? Lucky you. LOL

 

[Dan Thompson]

Making ZCI's? Now there's a thought. I did watch the other videos and plan to take a look at Keith Rucker's channel. I have watched other videos he has posted. Talk about old iron. Sort of like the small 4" surface grinder I have only on a larger scale. My grinder is so old it was made here in the USA in CT.

I'm not sure I'm brave enough to pound on the gib with a hammer. Maybe if I buy a spare.

 

[B2]

I recently purchased a PM833TV mill and I think I have a problem with the alignment of the mill. I have measured the tram on the Y-axis and found that there is 0.0035" of column tilt (or head nod) if you prefer.

@Dan Thompson
Hi, I just noticed your posting and I am curious about your measurement of 0.0035". ( I will call this a tilt of the column rather than a nod and I prefer to think of the nod concept as a motion of the head during the cutting process, rather than the column not being square to the table.)
Over what distance did you measure the 0.0035". If you specify the distance then this tilt becomes an angle and has more meaning. 0.0035"/10"=0.00035 radian= 0.02005 degree. (That is the angle away from 90 degrees, with respect to the z and y axis. Obviously, there can also be a tilt angle error along the z and x axis.).

Lets assume for a moment that you measure the change, 0 to 0.0035", as you move the indicator upward 10" as referenced to a square on the table. If the column base is say 5"x5" then it would mean that to correct the tilt you would need a shim of (5"/10")*0.0035"= 0.00175" placed at the edge of the column face. This is a very thin shim and so you may find when you take your column loose from the base some pieces of oil impregnated paper, which is sometimes used to fabricate the shim! If you do I suggest you measure its thickness and make a note as to location of each of the shims and the thickness so you will know your starting shims for "both" tilt angles ....Don't just throw the paper away!

By the way, if you want a cheap source of small thin metal shim pieces you cut open and remove, and measure the thickness of, the loose metal (magnetic) piece that is contained in the commonly available (white plastic) anti-theft tags that are placed on merchandise at stores. It is commonly about 16-20 microns in thickness so is less than a mil. (a 0.001"=25.4 microns). There is a second piece of thicker metal in these anti-theft tags, which is a bias magnet, and is made by role milling. It usually has glue on it to keep it stuck to the plastic container.

Good luck.
Dave L.

 

[Dan Thompson]

Hi Dave: I measured the deflection across the width of the table (i.e. along the Y axis). This was done by using a dial indicator in a holder held in a collet in the spindle. So by my calculation, the result is: arctan (0.0035/9) = 0.02228 degrees. I haven't measured the deflection along the Z axis since I don't yet have an accurate enough square to measure this. I have ordered a granite square to use for this and it should arrive in a few days. I have also ordered an assortment of SS shim material (0.001 - 0.006) which should arrive soon. In the mean time I have used some brass shim stock placed under the two front corners of the base. Access is a bit limited because there is only a narrow space between the front of the base and the end of the Y-axis ways. I don't think shimming in this manner is a particularly great solution as it greatly reduces the bearing surface area between the column and the base. It would have been nice if the factory had bothered to machine the column and base square in the first place. One would think they must have the necessary equipment to do so.

 

[Dan Thompson]

That was a bit unclear. What I meant was space between the bottom front surface of the column and the end of the Y-axis ways. Also, the brass shim was placed under the front corners of the column.