[Newbie] Tramming my PM-728 mill

[maticulus]

I've had the mill for a couple of weeks now and finally received the squaring tool to start checking setup so I can prepare to start using it. I watched two videos on tramming, on what appeared to be knee mills at a minimum and I read the instructions provided with the machine.

First, I locked everything down, gibs and quill and used a small flat magnet as 0 point for both gauges on the table, setting one and rotating the second gauge to that point for zeroing and then back to its position. I removed the magnet, lowered the head stock making contact with the table and checked the error. I got close but needed more repetitions to get the feel of the backlash and effects of loosening and tightening restraints.

I then tried the approach outlined in the manual, using the fine adjustment for the spindle and a 1-2-3 block, and that turned out bad with marked variance increase next to the previous result.

Somewhere in the process I came across info stating I should make the adjustment with the spindle near the position it would mostly be used. I did that, involving the fine feed again, but still didn't like what I was seeing.

Finally, lowered the head stock until the gauge tips were just above the table, zeroed using the magnet and then used the fine adjustment to cover the short distance while all else was locked down. The end result is what's seen in the pictures.

I relieved the pressure on the gauges, cranked the air conditioner for about an hour while it all sat. I went back to check it before taking it down and the gauges were off by .0015, X and Y.

I know temps affect specs, but I'm not sure that's the case here. There may have been a 4 deg drop in temps.

I welcome recommendations on how to approach the process with this machine, headstock vs. fine feed for example, while keeping in mind a good quantity of patience is needed.


About me; I'm an enthusiast and have been discovering and creating in electronics and mechanics since I was a kid, back when television went to bed to. Purchasing a mill is a continuation along the same path of discovery and creativity. My motto, except where it's very dangerous, "If it's already broken, all I can do is risk fixing it.".
Informal skills I've acquired as a result: auto diagnostics, engine and transmission building, mig welding, decent home HVAC repair and one outboard motor rebuild to name a few.

 

[Eddyde]

First, Welcome to HM!
I read your problem and am a bit confused. Both pictures show the indicators at the same 0, at what point are you getting the 0 0.0015" error?
Also in the beginning, I would remove one of the indicators and learn to tram it conventionally before using two. IMHO the double indicator arrangement introduces the possibility of error in the tramming tool itself. Yeah with one indicator you have to look at it from the backside or use a mirror but its much more reliable.

 

[maticulus]

First, Welcome to HM!
I read your problem and am a bit confused. Both pictures show the indicators at the same 0, at what point are you getting the 0 0.0015" error?
Also in the beginning, I would remove one of the indicators and learn to tram it conventionally before using two. IMHO the double indicator arrangement introduces the possibility of error in the tramming tool itself. Yeah with one indicator you have to look at it from the backside or use a mirror but its much more reliable.

Hello and thanks for the response. The pictures are of the initial apparent success on the X axis and then rotated 180 deg to show the same reading on the Y axis. The .0015 error noted on a follow up check before removing the gauge after sitting for a while with nothing changed, is not shown.

I agree with your assessment and was actually considering the possibility of the gauge dials being the source and will check the status using a single gauge.

Once this is addressed satisfactorily, I'll move on to the vise.

I'd like to add for those considering the purchase of this mill, that it now comes pre drilled for the Precision Matthews DRO after observing holes in the appropriate mounting points, PM confirmed this. The DRO costs the same whether they install it, or you install it after the fact so that's something to think about if you intend to use the PM DRO unit.

While checking full travel length of the table, the oil supply line on the machine's right side was pinched and perforated due to its "T" location, so be mindful of that.

 

[maticulus]

I took the conventional approach as you recommended and turned the gauge facing outward to make viewing it easier and the results without having made any adjustment since the initial favorable measure returned to the previous thumbs up outcome. Pardon the backlash on the camera angle, well as my decision to ignore the lack of lighting. The pictures represent both sides of the table though it's hard to discern.
There are two, but the same block and corner was used for each side. From now on conventional will be my preferred method.