# Quill downfeed on bench mill



## Driveslayer45 (Oct 15, 2019)

Hello All,

I've had a PM727V for several months and loving it, except for one part. The down feed of the quill seems to be inconsistent. as i feed down the quill will stop dropping then will 'drop' to catch up. i have contacted PM and they indicate this is normal as the quill is 'dropping' to take up backlash in the worm gear.  intellectually I understand this response and it makes sense.  practically its driving me nuts. This is my first mill as I am coming off of an old import 3 in 1, but that 3 in 1 doesn't exhibit this behavior. I have been told to snug the quill lock (on the left) to prevent or minimize this.. maybe I just cannot get the feel for it.

What is everyone else doing, are we just living with it, is there an adjustment to make, how snug are you making the lock ..

Any input is appreciated as sometime I have to work the quill back and forth to get it to the depth I want.  Also I assume this isn't a problem when I am actually cutting as the pressure of the material will take up the backlash ..

Thanks much


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## RJSakowski (Oct 15, 2019)

I don't have a PM but what you are describing doesn't seem right.  My mill drill has a return spring which always keeps the quill at the upper position.  Gravity should not be sufficient to pull the quill down, only user applied downward force.  Spring tension is adjusted until this is so.


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## RJSakowski (Oct 15, 2019)

The return spring is on the left side of the mill.  Your manual shows how to adjust it on page 18.


			http://www.precisionmatthews.com/wp-content/uploads/2017/06/PM-727M-V-4-16-2018-v4-Web.pdf


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## Driveslayer45 (Oct 15, 2019)

So the return spring is where I started, I tightened it up, a lot, and still had the problem but in doing so I introduced another; sometimes, with the spring tight, the quill would stop going down when i turned the feed dial.. i would have to loosen the engagement knob and retighten it.. effectively the clutch was slipping.

I was advised to loosen the spring till it would lift the quill, but no more. i loosened it which cleared up the issue i caused, but i still have the problem that caused me to tighten the spring in the first place.


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## RJSakowski (Oct 15, 2019)

Driveslayer45 said:


> So the return spring is where I started, I tightened it up, a lot, and still had the problem but in doing so I introduced another; sometimes, with the spring tight, the quill would stop going down when i turned the feed dial.. i would have to loosen the engagement knob and retighten it.. effectively the clutch was slipping.
> 
> I was advised to loosen the spring till it would lift the quill, but no more. i loosened it which cleared up the issue i caused, but i still have the problem that caused me to tighten the spring in the first place.


OK Driveslayer,  I owe you an apology.  I went down to look at my mill and found that I had made a modification, likely to cure the same problem that you are experiencing.  I made the mod more than thirty years ago and frankly don't remember it.  But the spring isn't in the parts diagram so I must have.

The Quill return spring is a constant force spring which provides the restoring force to the pinion shaft.  It does not account for back;lash in the pinion gear/rack.  In that regard , the quill will take up the lash in the downward position.  As you start to move the quill down, the quill will hang up until the lash is removed and then start to move.  If everything is loose enough, gravity will pull it down agaqin taking up the lash.  This the the erratic motion you are observing.  There are to ways to eliminate this.  

One is to loosen the quill up so that gravity will always pull it down, the extent being controlled by the pinion gear.  This is not desirable as when end milling the are additional forces pushing the end mill and therefore the quill up.

The second way is to slightly tighten the quill lock.  This provides additional friction which counteracts the gravitational pull on the quill and the quill only responds to the force provided by the pinion gear.  You will still have backlash and to that end all final quill adjustments should be downward. 

A third way is to mod the machine. I attached a heavy extension spring to the back of my quill with the other end anchored high inside my head.  The spring is strong enough to counteract the gravitational force Thought the travel range of the quill.  Checking my quill, I have smooth travel over the range of the quill.  There is about .011" of backlash but since I make all my quill adjustments downward, it only comes into play when I am retracting the quill.


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## Driveslayer45 (Oct 15, 2019)

RJ that is beautiful, thank you for sharing that and taking the time to look at your own setup.  It is comforting to know that this is a common symptom, now i just have to figure out the best way to fix it for me.  like you i prefer to make all my adjustments during the down feed as well. thank you.


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## pontiac428 (Oct 15, 2019)

My Rong Fu does what you describe.  I cut the amount of backlash by 2/3 by loosening the mounting bolts for the quill feed R&P and adjusting the tooth engagement using the oversized slop in the bolt holes.  When the play was almost gone, I tightened everything back up and have been appreciating the difference ever since.  Else, there are some ideas out there for using a gas strut or a weight and pulley to force the quill to one end of its backlash.  The remaining backlash that I do have I work past by finding my number and locking the quill tight.


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## T Bredehoft (Oct 15, 2019)

I had that problem with my PM25, I  instaled a brass button backed by a stiff compression spring inside the quill clamp. By feeling where the spring is totally compressed, then backing off a bit, I put pressure on the quill to keep it from dropping.

_Edit:_ correct typo.


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## higgite (Oct 15, 2019)

I have (or had) that problem with my LMS 5500 (Sieg SX2.7). I discovered it when trying to plunge mill some blind holes to a specific depth. I used the fine feed to feed to the depth I wanted, but I didn't stop the spindle. In a couple of seconds, the EM had plunged a few thousandths lower than when I stopped feeding it. I fought that shortcoming for awhile by s-l-o-w-l-y downfeeding when I got close to my target depth. Then I added a quill stop which I can preset at my target depth. No more problem.

Tom

Edit: The same problem was also discussed in this thread: https://www.hobby-machinist.com/threads/perplexed-a-little-help-needed.79163/


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## Driveslayer45 (Oct 15, 2019)

Thanks for the feedback everyone.
Pontiac - taking out the excess backlash is something i am interested in tryin to figure out how to do on this machine.

T B - i was thinking of doing something similar but i think the 727 uses a squeezing clamp to lock the quill.  I am looking for a stiff spring that will go over the shaft of my quill lock so i can use it to keep some tension on my quill, then still be able to tighten down to lock the quill, fully collapsing the spring.

H - i have experienced the same thing and it is very frustrating. I've ruined a few parts before i figured out what exactly was happening.


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## pontiac428 (Oct 15, 2019)

@Driveslayer45 Backlash can be improved by loosening the bolts I marked and sliding the outboard assembly down towards the table.  Work the quill feed lever back and forth within the backlash zone while you are adjusting so you can feel what you are doing.  Then tighten the bolts back up and check the full range of quill travel for tight spots.  There's a happy medium there.  Now do the same type of fitting, torquing, aligning, and adjusting to every part that touches another part, and you'll have a decently performing little mill!


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## Driveslayer45 (Oct 15, 2019)

Thank you. if I get shop time tonight I will do that.


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## Driveslayer45 (Oct 15, 2019)

Pontiac that was a great recommendation, it took my backlash from .016 to .009


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## pontiac428 (Oct 15, 2019)

Glad to hear it. There is a lot of adjustment in these import machines that you can take advantage of. It's up to the owner to tune the little beasts, but there is a trove of capability and hidden precision to be eked out.


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## Tom1948 (Dec 2, 2022)

I someday found that when milling aluminum, something I mostly do the end mill wants to grab. If I run the mill a little faster It does not grab so much thus pulling the quill down. I have had the same problem as you have. Now, another helper spring makes sense and i intend to install one someday. I have to really crank down on the quill lock when milling also. One of these days i will get around to investigate it. Maybe  another bushing inside. I have also rigged up a dial indicator and if i need to get "dead nuts on " I raise the quill a bit and come back to it.  It should not have to be that way. The dro should work as it is supposed to, but otherwise i love my 727.


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## Jason812 (Dec 3, 2022)

I plan on doing something similar to what RJ did on the PM833.  Its my biggest beef with the machine.  I had a Harbor Freight drill press given too me that doesn't have this problem.   I don't see why it can't be solved on these machines.


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