[BobRock]

I'm setting up my bench top mill, a Precision Matthews PM-727M w/DRO, and I'm curious about how close is close enough for typical DIY gunsmithing?

Specifically I'm thinking about how square the column and head is to the table. Better is always better. But is .001" over 8" "good enough?" Do you guys align to better than that?

I'll be able to adjust the head's rotation easily enough. The column will need shims if it needs to be more square. The head's "nod" will need shims, but won't be easy.

 

[Integrity Arms]

I am assuming it has lockdowns for the column? You are not going to be able to cut any
closer than .0005 on a hand crank bench mill anyway so .001 in my opinion over 8" isn't horrible, but I'd get it down to .0005 if possible.

 

[seagiant]

Hi,
I built one of these spindle squares and it WILL let you know when you are "dead nuts"!!!

 

[BobRock]

I built one of these spindle squares and it WILL let you know when you are "dead nuts"!!

I’ve seen jigs like that. Do they offer any advantages, other than fast setup and reading, over an indicator held in a collet swung across the X and Y axes?

 

[BobRock]

I am assuming it has lockdowns for the column? You are not going to be able to cut any
closer than .0005 on a hand crank bench mill anyway so .001 in my opinion over 8" isn't horrible, but I'd get it down to .0005 if possible.

Yes, it has X, Y, Z, and spindle locks. I’ll see if I can get it to .0005 over 8”.

 

[Integrity Arms]

Yes, it has X, Y, Z, and spindle locks. I’ll see if I can get it to .0005 over 8”.

Do you have a tramming indicator?

 

[BobRock]

Do you have a tramming indicator?

Yes, I have a Starrett The Last Word and another Starrett at .001” per revolution. I can get them mounted from a collet and then swing them across the X and Y axes.

 

[Integrity Arms]

Yes, I have a Starrett The Last Word and another Starrett at .001” per revolution. I can get them mounted from a collet and the swing them across the X and Y axes.

Wow you bought the good stuff lol..

 

[BobRock]

Wow you bought the good stuff lol..

eBay! I found some good deals on used gear that had been cared for well.

 

[seagiant]

I’ve seen jigs like that. Do they offer any advantages, other than fast setup and reading, over an indicator held in a collet swung across the X and Y axes?

Hi,
I've done it both ways and the spindle square (to me) is easier and more accurate!
I just made one, down and dirty, nothing fancy and used 2 indicators from HF.
Works great!!!

 

[Integrity Arms]

I’ve seen jigs like that. Do they offer any advantages, other than fast setup and reading, over an indicator held in a collet swung across the X and Y axes?

This is what I was wondering if you had. Amazon actually sells one that goes from 3-6 " for $89 They cut head tramming down to about 25% if the time compared to the way your doing it.

 

[wrmiller]

Nice choice on the mill. But I have two PM machines, so I may be a bit biased.

Chasing zeros when setting up a machine can be a hobby for some, or a religion for others. On a small bench mill I recommend getting it as close as you can, but don't go stupid. For example, I would consider a thou over 8" of travel 'good enough' for most work. My reasoning? Put a DTI in the spindle of that mill and then gently push back and forth on the head and watch your needle move. A lot.

One of my hardest lessons to learn when I started out was that 'everything flexes' when machining. The machine will flex, the cutter will flex, and the material (depending on setup) will flex. Trying to minimize this flex in a small machine can be a maddening process.

May I suggest that you go to the hobby-machinist.com forum and visit the PM sub-forum. There are a bunch of PM owners there (including me) that can help with machine specific questions. And the other non machine specific sub-forums can be a wealth of information regarding general machining and other related questions.

 

[BobRock]

May I suggest that you go to the hobby-machinist.com forum and visit the PM sub-forum.

I will do just that! Thanks for the pointer.