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PM25MV Nod adjustment suggestions

Discussion in 'A BEGINNER'S FORUM (Learn How To Machine Here!)' started by Bill Kahn, Jun 25, 2017.

  1. Bill Kahn

    Bill Kahn United States Iron Registered Member

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    I've had my PM25MV mill for a week now. Having a great time. I have the first pass adjustments made now.

    Have begun by making a 1.5" aluminum cube. (Hey, gotta start somewhere). I have a 1" diameter end mill, so it takes two passes to get to 1.5".

    When I was indicating for the head tilt adjustment (got that pretty well set) I did note that I had 3 mil of nod over 8".

    Well, it turns out that is enough to to great a noticeable lip between the two X-passes. I am not sure how big it is, but my fingernail can feel it. And it is quite visible. Calculation suggests it is .3 mil.

    I would love to adjust this out. But the Precision Matthews manual says this is not as routine as adjusting tilt. Seems to involve shimming the underside of the column.

    For other hobby mills, when you do two overlapping X-passes (in my case 7/8" apart), can you feel a lip between them? What should me expectations be?

    Does anyone have any experience? Suggestions? Any YouTube videos? Horror stories? Is this something I should stay away from or just dive in and it sort of will reveal itself as I get into it?

    Thank you.

    -Bill
     
  2. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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  3. Bill Kahn

    Bill Kahn United States Iron Registered Member

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    Well, actually this was helpful. I have ordered some shim material and what the heck. How hard can it be? Loosen some bolts. Lift a hair with the the 99$ HR engine hoist, slide two mil (.002") under the front. (No fancy epoxy. At least for this round.) Gently lower down. Rebolt. Retram. Assuming I don't drop the whole thing onto the garage floor I'll bet I can have it done in a couple of full weekends. (I'm in zero rush. It is all just journey.). Thanks again. -Bill
     
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  4. Bill Kahn

    Bill Kahn United States Iron Registered Member

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    OK. I did it. I adjusted the nod on the PM25MV. Measurement and calculation suggested I would need .002" under the front of the column. How hard could it be? Just followed the above plan. The 10mm hex bolts bolting the column to the base were pretty tight but a large Allen wrench got them lose. Always a bit exciting to use the hoist. Added a front strap to prevent the mill from lifting the back first off the base. I needed it to lift front first. Got it up half an inch. Slid in some .002" thick stainless steel shim. 1" deep. 6" wide. Cut away a hair at both ends for the front bolts. Lower. Rebolt. Crank down and really tighten. (And a bit more unscrewing here and there to get easier access. It is so satisfying working on a machine I can understand with tools I can afford--like wrenches.)

    Was not a surprise I had to retram the tilt. Then measured the nod. And, low and behold, not only did I not drop the mill on the floor, but I removed most of the nod. I still have .001" over 8". Maybe the stainless steel compressed some. I do have some .003" shim. I guess I could do it all again to try to get to perfect. But given I have .002" tilt still over 14" the nod is close to the same size error. So, I will declare it good enough for my projects.

    I will see how bad the ridge is when facing with multiple passes.

    I wonder how would one engineer a mill of this physical capability that had easy fine-tuning of tilt and nod. Tuning needs to stay locked in and be stable over many months. And yet was fully rigid for the work it is designed for. I accept it would be more expensive. But I just wonder what the engineering would look like. Tilt adjustment I may do now and then. I bet I may not ever do nod adjustment again. It took me four hours from start to end. Maybe I could get it down to two hours. Still, it is a project of sorts for a fellow of my beginner skills.

    -Bill
     
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  5. British Steel

    British Steel United Kingdom Active User Active Member

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    A tilt adjustment could be as simple as long grubscrews in the column-base casting with locknuts, similar to flat gib adjustments, the hard way would be to individually scrape in the mating faces with some accurate measurement going on (how they do it at the high end of the price spectrum!) for a permanent setting? Ideally no adjustment would be necessary until the machine's due for a rebuild (moving parts will wear, the base casting won't), assuming the machine's rigid and starts out square and true!

    Dave H. (the other one)
     

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