# Pocket milling



## ChipsAlloy! (Sep 22, 2014)

I was wondering how you guys achieve a precise depth when machining a pocket in a part . Of course I'm talking about a job done on a pm932/45 hence the post in this section. 

I would venture saying that you use the crank to lower the head (cutter) into the material because I normally raise the knee when at work. But I might be wrong. Is there another technique for these smaller machines ? Like maybe there is a way of using the quill and control the descent ?

 I do have the z axis on my dro so I can tell how much I lowered the head with the crank. I guess I am wondering if there is a better way than the one I figured.


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## mattthemuppet2 (Sep 23, 2014)

I'm trying to avoid doing work so I'll give it a shot, even though I'm no expert (ha!) 

I'd plunge to 80% of depth with a center cutter using the quill, use a rougher (love 'em!) to get most of the pocket out, then a finisher to end and side mill the pocket to depth and width. Set the quill to depth, lock and go to town  It's probably not the quickest way to do it, but it should help with chips too. 

How deep is the pocket? Within the range of the quill travel?


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## darkzero (Sep 23, 2014)

With my PM45 I use the quill "fine feed" handwheel to plunge with DRO for measurement. It's not a very rigid quill so I try to limit quill extension by lowering the head ahead of time to compensate. I have a DRO for head Z axis also but I find it to be pretty much useless.


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## ChipsAlloy! (Sep 23, 2014)

Fine feed of the quill... Hmm I will have to check that out using the handwheel. I will try it this evening and see how it goes. 

So Using the head crank may not be the way to go for that job. In that case Dark, you might be right the z axis would be pretty much useless.

But for now I have to go to work..


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## ChipsAlloy! (Sep 23, 2014)

mattthemuppet said:


> How deep is the pocket? Within the range of the quill travel?



Yes it is about .375" deep in aluminum so well within quill range.

I admit I was afraid of doing it with the quill because lowering it by hand I would not have much control ( can go too deep if the cutter bites into the piece or even big vibration) .

Now I cant wait to try with the fine feed and see how it goes.


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## wrmiller (Sep 23, 2014)

Pocket milling on these little bench mills is the worst case scenario in my opinion. I too am used to/learned on a BP with a scale on the knee, so naturally I got used to raising the part into the cutter for operations like this. On my PM I have a scale on the head and normally just drop the head slightly below target depth and bring it back up so that I have a consistent load on the Z-axis screw (and subsequently locking the head down of course. However this sequence doesn't work for pocket cuts.

But in talking to someone else who has a larger machine/larger quill, they use the quill to plunge the cutter into the part when making pocket cuts. My only concern here is 'axis creep' whereby the cutter falls slightly lower during the cut due to slop in the quill mechanism as downward cutting pressure on the tool is reduced as material is removed. I guess you have to lock the quill to prevent that from happening, but then what happens when you unlock the quill? Do you have to stop the cutter before doing so?

Bill


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## zmotorsports (Sep 23, 2014)

I will admit this was one of my concerns when I had originally ordered the PM932PDF as I too am used to locking the quill and raising the knee precisely where I need it for roughing and then finishing cuts. I figured I would just have to figure something out once I got the machine as my budget and room really couldn't accommodate a full-size BP/BP clone.

It is interesting to read how you guys are compensating for this and dealing with the head vs. knee type of movement.  

I just wanted to subscribe to make sure I didn't miss out on useful information.


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## JimDawson (Sep 23, 2014)

What I did to compensate for the quill feed backlash is to counter balance the quill it's self.  I am using a cable that is connected to the quill stop that runs back to an air cylinder that provides a constant 50lbs of up force on the quill.  http://www.hobby-machinist.com/show...CNC-Conversion&p=199564&viewfull=1#post199564  This takes all of the backlash out of the system in both CNC and manual mode.

Using this system it seems to hold about 0.0003 when in CNC mode, at least that is what the DRO says.


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## Falcon67 (Sep 23, 2014)

darkzero said:


> With my PM45 I use the quill "fine feed" handwheel to plunge with DRO for measurement. It's not a very rigid quill so I try to limit quill extension by lowering the head ahead of time to compensate. I have a DRO for head Z axis also but I find it to be pretty much useless.



Same here.  Have a 6" digital scale on the quill, and use the fine feed.  The scale is required on my Griz because the fine feed falls behind about .002 every inch or so of downfeed.  You'd lose track real quick using the micrometer dial.  There's almost no backlash in the fine feed and for maybe .3 in either up or down the dial is dead on.  Go an inch, you are off .002.  Another inch, now your .004 off.  Etc.


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## wrmiller (Sep 23, 2014)

Falcon67 said:


> Same here.  Have a 6" digital scale on the quill, and use the fine feed.  The scale is required on my Griz because the fine feed falls behind about .002 every inch or so of downfeed.  You'd lose track real quick using the micrometer dial.  There's almost no backlash in the fine feed and for maybe .3 in either up or down the dial is dead on.  Go an inch, you are off .002.  Another inch, now your .004 off.  Etc.



That seems kinda weird Chris? Metric screw or rack and Imperial dial?

This morning Paul at CO told me that they put the Z-axis on the quill on their manual machines. That would require me to do this like you guys, i.e. move the head close then use the quill for precision movements. I will have to chuck up some test pieces and quantify exactly how accurate this method will be. I hope the 12Z comes with a digital on the quill, so I don't have to depend upon a dial. If not, I'll put a cheap one on until I can afford a DRO. I've bought too many machines and tools this year and my 'fun money' is about gone.  

Bill


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## Falcon67 (Sep 23, 2014)

It just is.  The downfeed is scaled in .001 imperial.  Griz replaced the parts - no change.  Probably something on the quill or the rack.  It's a rack and pinion drive, I'm amazed it's that accurate over even a short range.  I'll try to get a better pic, but my 6" scale was cheap and almost no engineering.







$30 - https://www.grizzly.com/outlet/6-Digital-Scale-Inch-Metric-Fraction/T23015


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## ChipsAlloy! (Sep 23, 2014)

Thanks for the answers this is interesting.

Well I had a bit of time to try the fine feed on the quill. I have not actually machined the pocket yet just played with the components.

So I used the manual feed handle (fine) to lower the cutter. Then while I was still turning the handle, I slowly tightened the quill lock. It was kind of a simulation to see what happens when the cutter starts cutting and there is some pressure applied. I then release the lock and boom the quill goes down a good eight of an inch. You can clearly see it lower in one shot. So that would be the backlash in the fine feed? Or am I doing something wrong?

  Because it sounds like a lot, I would not be confident in doing pocket milling like that. I would guess the cutter might move up and down at a high frequency leaving poor finish and accuracy.

Tell me what you think


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## darkzero (Sep 23, 2014)

ChipsAlloy! said:


> So I used the manual feed handle (fine) to lower the cutter. Then while I was still turning the handle, I slowly tightened the quill lock. It was kind of a simulation to see what happens when the cutter starts cutting and there is some pressure applied. I then release the lock and boom the quill goes down a good eight of an inch. You can clearly see it lower in one shot. So that would be the backlash in the fine feed? Or am I doing something wrong?



Not sure why you would use it that way but that would be expected as you are putting load on the leadscrew doing that. I don't use mine that way. When I plunge as if milling a deep slot, I plunge to depth using the fine feed, then lock the quill without turning the fine feed anymore after that. I only lock the quill when taking a roughing/heavier cut. Then when I get close to my final depth, I plunge, again with the fine feed & make the finish pass without locking. On light cuts like for finishing the quill does not move with fine feed engaged & the quill not locked, provided that the setup is proper, rigid, no chatter, no vibrations. And if for some case I do need to lock the quill hard for a finish pass, I'll compensate for the amount that it might move.

Depending on how far my quill is extended, if I lock the quill hard it will move (according to my quill DRO) a 1/2 thou to a thou. Then if I unlock it, it will move back roughly the same amount or 1/2 thou more. If I lightly lock the quill, most of the time the DRO does not indicate movement at all (in the Z axis anyway). So when I lock on a roughing pass, if it's a heavy cut I'll make sure the lock is firm, yes it might move a bit but it's a roughing cut so doesn't matter to me. Not really any different than my table, locking either axis will indicate movement on my DRO but not nearly as much as the quill, couple to few tenths.


These are the very first things I made with my PM45. Chip pan rails for my old bandsaw. I miscalculated at first & to the left you can see my first starting slot which I plunged & milled using the method I explained above without any problem, as well as finishing them off








Not really a good example but here I also did the same, I did not plunge all the way through & mill the slot in one pass, I plunged halfway, then plunged through on the next pass.








Just a couple of days ago I finished this adapter for my RT. I don't have counterbores so I milled the counterbores by plunging with an endmill. I plunged with the fine feed to depth, then backed out. They came out great.







To add & not that it matters, my PM45 is a power downfeed model and was from the batch just before the PM45s & PM932s were offered with quill DROs. The PDF model does not have the depth indicator. I used an 8" Mitu scale & I prefer mine this way.







Every type of machine will have their advantages & disadvantages, a "perfect" machine is expensive! That's just the nature of their design whether good or bad, I would say get to know your machine & don't expect it to do something it's not capable of. If you can't live with it, time to get a replacement. I've learned a lot about how my machines behave & function & compensate for the things I might not like. Although I would like a full size knee mill someday & a 14-16x lathe I'm still very happy with what I have now as they haven't let me down yet.


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## zmotorsports (Sep 24, 2014)

darkzero said:


> Every type of machine will have their advantages & disadvantages, a "perfect" machine is expensive! That's just the nature of their design whether good or bad, *I would say get to know your machine & don't expect it to do something it's not capable of.* If you can't live with it, time to get a replacement. I've learned a lot about how my machines behave & function & compensate for the things I might not like. Although I would like a full size knee mill someday & a 14-16x lathe I'm still very happy with what I have now as they haven't let me down yet.



I completely agree Will.  That is with ANY machine as they all have their little idiosyncrasies.  Even our full-size BP clone at work is not without its' little quirks.  

With my old lathe I knew exactly almost by feel without looking at the dials how much it could handle for roughing cuts and then even though the dials were not very accurate I could get within a thou by the dials.  If/when I needed to be closer I used the soft stop or set up a dial indicator.

With my new lathe I am getting a feel for the accuracy right off the bat and can dial right in once I get my reference cut and it is spot on.  But like you said, there is a learning curve and you are trying to get to know the machine and anticipate its' response to every input you give it.

By the way Will, nice work on the examples.  Very nice.


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## ChipsAlloy! (Sep 24, 2014)

Thanks a lot for the answers Dark. I appreciate the time you spent and with your explanation of how you actually do it I understand better.  

Now for another question : What makes it that you prefer using the quill instead of the head crank?  Easier to fine adjust depth even if you have dro on z axis? Or is it that moving the head up/down affects in a way the x/y position of the cutter ?(i know it shouldnt but maybe on our smaller machines).


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## Falcon67 (Sep 24, 2014)

I prefer to use the head crank for rough adjustment, as in going from a drill to a tap setup on the same hole, or drill to collet + mill for a countersink.  I use the head to get close, then lock the head and use the fine feed on the quill for the real work.  On my square column, I do not seem to lose registration.  I just move/lock for every operation that needs the head moves and the head should be in the same relation to the table.  Saying that, knowing the machine sits unlevel and un-trammed right now.

Better pics of DRO, very Q&D install:


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## darkzero (Sep 24, 2014)

ChipsAlloy! said:


> What makes it that you prefer using the quill instead of the head crank?  Easier to fine adjust depth even if you have dro on z axis? Or is it that moving the head up/down affects in a way the x/y position of the cutter ?(i know it shouldnt but maybe on our smaller machines).



I'm not sure what the "correct" way is to use these types of mills but this is how I see it. The only other vertical mills I have used were BPs. Lets take into account that we did not have DROs.....

On a BP or other knee mill, the knee is commonly used for measured Z depth/height adjustments as it has a dial on it. Although BPs have a quill handwheel for feed (although many don't even have them on their machines) the quill does not have any type of dial for quill, well except for the depth stop. I don't see it common practice to use that "dial" on the depth stop for measurement but I suppose that's how they designed it to be used? The knee dial is much more accurate.

Now on these RF-45 style & similar mills, of course there is no knee that moves. It's the complete opposite of a knee mill, the head moves for the Z axis with the table height stationary. Well on most RF-45s, if not all that I have seen, there is no dial on the Z head crank. So how would you measure Z head movement (again assuming we don't have DROs & are not using added mag base dial indicators). The fine feed does have a dial on it (although not very accurate), so I assume they intended for the quill to be used for Z measurements.... well somewhat.

I don't use the head crank cause for me it's not practical. If I need to move the Z using the head say a few thou or so, it's too much trouble. On My PM45, the head crank is on the left side of the column. My DRO display is on the right side of the column, kind of hard to crank the head with precision & read the DRO at the same time. Some RF-45 clones have the head crank on the right side which would be easier but most are on the left side. Well the DRO display could also have been mounted on the left side but I prefer it on the right as I have a power feed on the left side of the mill for the X axis with no handwheel there.

Not only that, I have not added any head counter weight mods like some of the guys do using gas shocks. So cranking the head up is much harder than cranking down as the head is heavy. Now when I move the head I like to drop it down to roughly where I need, then I'll crank it up slightly & lock it. I never lower it & leave it at that without slight cranking back up. I always lock the head before I need to take a cut that matters. On my mill, locking the head moves more (according to the DRO) than any other axis that is lockable. When I tram I set the nod with the head locked so doing so gives me the most accuracy.

Because of how I need to make Z measurements I sometimes wish I did have some sort of knee mill. But then again I don't when I think about the times I used BPs for an entire day. On my lathe, I have the spindle centerline set to my elbow height. That's what I was recommended for minimal fatigue & it does work for me. So with my mill, I set the table at elbow height. So no back aches having the bend over when the knee is dropped way down. Well I'm still young but I do have a beer belly to worry about.


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## wrmiller (Sep 24, 2014)

When I bought my PM25, I discussed this with Matt (owner) and he and I do basically the same thing when a 3-axis DRO is installed.

With the quill fully retracted, move the head so that the cutter is close to the surface to be cut. Gently lower the quill manually until the cutter just touches the work surface and lock the quill. Zero the z-axis on the DRO and 'bump' the cutter off the work surface a few though or so. Move the cutter off the work surface and then drop the head below your target depth using the z-axis wheel and then bring the head up to your target depth. Lock the head and cut.

By always coming up to your cutting depth, the head/screw interface is loaded the same way each time. Or at least that's what I tell myself. With a scale on the head, you are measuring absolute position anyway so coming down or up probably doesn't matter much.

But to cut a pocket like the OP is talking about, I would probably use the quill to (hopefully) control the DOC better. Not having had to do that yet means this is just speculation on my part.  

Bill


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## ChipsAlloy! (Sep 24, 2014)

Thank you guys , learning stuff right now!


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## bartives (Mar 22, 2015)

My PM-45 did not come with the quill DRO, where do you get the cast iron bracket that attaches to the quill and DRO?


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## darkzero (Mar 22, 2015)

bartives said:


> My PM-45 did not come with the quill DRO, where do you get the cast iron bracket that attaches to the quill and DRO?



I got it from Matt. Check out posts 27 & 139 in my PM45 thread:

http://www.hobby-machinist.com/threads/my-pm45m-pdf.9885/page-7#post-242436


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