[How-To] Improved Tramming for the PM-833T

[ahazi]

It started to look like my PM-833T got out of tram so I decided to check it out. I pulled out my tramming gauge tool and it was off.

I started the X-axis tramming process by releasing the three 19mm nuts (left, right and center) that hold the mill head to the vertical carriage on the square column. It quickly occured to me that it will be a trial and error attempt to tram the head as every time that the nuts were tightened the reading changed.

I looked in the H-M forum and found the following useful posts about tramming a square column mill:
https://www.hobby-machinist.com/threads/tramming-my-absolute-newbie-mill.12013/#post-99423
https://www.hobby-machinist.com/thr...amming-a-square-column-mill.30803/post-264057
https://www.hobby-machinist.com/threads/tramming-my-pm-833tv.91530/#post-836911

I decide to make something similar as an aid for adjusting the mill head. My goal was to have a guide that is strong enough to move the head even when the nuts were slightly tight to avoid a back and force adjustment. My add on bars seem a little on the large side but they work very well...

The bars are 100 x 30 x 19 mm made from 7075 aluminium. The adjustment screw is 3/8-24 with a turned flat bottom, the screws holding the bar to the mill through a tapped hole in the casting are 1/4-20. With this setup it was pretty quick to bring the tramming to practically zero error and keep it stable while tightening the nuts.

The Y-axis does not have a specific adjustment for tramming and it is slightly off. I would like to know what is other users experience with tramming the PM-833T

Here are some pictures of my work:

Ariel

 

[Lucas E]

How well does it work? I built one that wasn't quite as heavy duty as that, and it flexed and really wasn't all that helpful. I eventually took it off and just bang the head around with a dead blow hammer until I'm blue in the face.

 

[davidpbest]

Looking good. Be sure to check the quill movement is identical to the head movement. More detail here - watch the referenced video. How far off is the X-Y perpendicularly?

 

[ahazi]

How well does it work?

It works very well

I built one that wasn't quite as heavy duty as that, and it flexed and really wasn't all that helpful. I eventually took it off

Your description of the failed "lightweight" solution is so encouraging. After looking at what others did, I felt that I might have gone too far. This one is very rigid. It is made with aluminium but 7075 aluminium is stronger/stiffer than some steels.

and just bang the head around with a dead blow hammer until I'm blue in the face.

This is exactly what made me build this, I did not like the dead blow hammer method...

Ariel

 

[ahazi]

Looking good. Be sure to check the quill movement is identical to the head movement. More detail here - watch the referenced video. How far off is the X-Y perpendicularly?

Hi David,

I checked both the quil movement and the head movement for squareness to the table and both look good, very minimal variation. Also the X-axis tramming is maintained while changing the height (Z-axis) through the quill or the mill head.

The Y-axis tram error is 0.0015" over 6". I think I can live with it for now.

Question: is the knee mill also as sensitive to locking the quill and the table height to get consistent results?

Ariel

 

[7milesup]

Ahazi... I have a question unrelated to the information you shared in post #1. What do you have for a quill downfeed wheel? Looks interesting.

Also, thanks for sharing your method for tramming and the link to tramming gauge tool. I need to do this with my mill.

 

[Lucas E]

It works very well

Your description of the failed "lightweight" solution is so encouraging. After looking at what others did, I felt that I might have gone too far. This one is very rigid. It is made with aluminium but 7075 aluminium is stronger/stiffer than some steels.

This is exactly what made me build this, I did not like the dead blow hammer method...

Ariel

Mine wasn't a whole lot thinner, and was made of steel. I was trying to dial it in to .0005" or less across roughly 12" and found the assembly had too much flex at that range. I was still fighting movement when I tightened the head. Are you shooting for that level of tram?

FYI low carbon steel has roughly 3 times the modulus of elasticity of 7075 aluminum. I.E. its 3 times stiffer

 

[RJSakowski]

I used a similar concept for tramming my Tormach PCNC 770. The mill was aligned at the factory and tapered dowel pins were used to hold the alignment. By removing one pin and using the second pin as a pivot, I could take advantage of the clearance in the bolt holes to make slight adjustments to the tram in the x direction. The adjustment worked but the tap it with a hqmmer, tighten, check procedure grew old fast. In response, I designed and installed the adjuster shown below on the side of my mill head.

The Tormach mill is different than a square column mill in that there is no quill. All Z axis movement is achieved by moving the head op and down. However, it is important to verify that the spindle axis is parallel to the z axis ways. Adjustments are made in two ways, depending upon what is out . If the column is not perpendicular to the x and y axes, then the base of the column has to be shimmed to correct. Once the column is correctly aligned, the standard tram measurement can be use to adjust the head relative to the column. Fortunately, in my case , the column was true. Tramming the head in the x direction was accomplished by rotation a described above. Tram in the y direction hd t be accomplished with the use of shims between the head and the z axis carriage.

 

[jwmelvin]

FYI [all] steel has roughly 3 times the modulus of elasticity of [all] aluminum. I.E. its 3 times stiffer

FTFY

 

[davidpbest]

Question: is the knee mill also as sensitive to locking the quill and the table height to get consistent results?

Ariel

Locking the quill, yes. Locking the knee to column, no (due to the weight of the knee). But with my RF45, I always locked the head to column because heavy milling could cause the head to cock backward by the amount of sloppiness in the head to column gib. In my case, after bluing and precisely fitting the gib, the head might cock backward by 0.001” during aggressive milling if left unlocked. That showed up when using large face mills as a few tenths difference in row-to-row flatness.

When you say you have 0.0015” in 6” for the Y, I assume you mean spindle to table surface measurement using your spindle square dial indicator setup. I would shim that out. Are the column-to-base bolts on the 833 accessible from above, or are the bolts coming up from under the base like on some of the bench tips? Have you checked that moving the table in/out in the Y direction doesn’t displace the table in X? That would indicate the saddle isn’t machined accurately. James (Clough42) found that on his 940, X and Y movements were not precisely perpendicular.