Warco A2F quill backlash - any pointers?

Hi all.

I have a Warco A2F milling machine, of 1999 vintage, so a later one without the feed gearbox (although it has an electrical power feed unit).

I have some problems with quill feed backlash, which come from I think three places:

- The rack/pinion combination that is attached to the quill rapid feed lever
- The worm drive that's used for the fine feed arrangement
- A poor fit on the keyway for the screw-in arrangement that's used for engaging the fine feed.

The last two I think I can do something about - re-cut the keyway in the toothed collar so it's less sloppy on the key, and make an eccentric bush for the fine feed handwheel arbor so the meshing can be adjusted.

I'm less sure about the rack arrangement though - I think there's damage to the rack on the quill itself, as at times there's a sudden drop of ~1mm when downfeeding, especially at the top of the travel - I can't easily adjust the meshing on that, and have not been able to get rid of this problem without the feel of the feed becoming very lumpy, which suggests to be excessive depthing of the rack/pinion combination and thus rapid wear in use.

Has anyone any experience with these machines or the very similar ones out there and could make some suggestions? I think this problem has existed ever since I've had the machine, but it's only recently started to annoy me enough to do something about it....

Thanks,

Youra.

I think first of all you need to disassemble the quill to look at the state of the rack and its pinion. May just be a bit of swarf.

Hi Youra.

I have an A2F from 1998 ,the backlash from the downfeed
pinion to the quill on my machine is .031 inch so not so much different
from your machine, it has always been like this from new.
Part of the problem is that the weight of the quill is unsupported ,the
return spring is on the pinion ,i altered my machine by fitting a loose pulley
wheel on the pinion shaft and machining a slot into the quill body and
using a thin stranded cable (1mm) routed it out the back of the head
casting to a gas strut which lives within the hollow tube .
This does require some extensive machining and modifications to
some of the parts of the head.
This worked well until the gas strut packed up ,a suitable spring
would do the job just as well . I altered the quill lock to a two part
aluminium part see photo that has a left and right hand thread so that it will
release properly and can be adjusted to give a positive feel when
down feeding.

You can inspect the pinion and rack fairly easily just by removing
the parts you have identified, the handle return spring is under the
cover on the handle side care is needed when removing
as the spring is under some tension make sure that you fit some
packing on the table under the quill as it will drop when the pinion
is removed ,check also that the quill locking pads are in the correct
position when you reassemble as they can easily be put back in
the wrong position and damage the quill.
Some other photo's of this machine in the album.

John

Thanks guys - I'll take a look and report back.

At first sight though, it seems the feed and clamp mechanisms have been extensively modified by a previous owner, so they don't look much like the drawings I've found for this machine.

John - I notice in your CNC conversion album that you've used the external depth stop as the basis for the Z-Axis drive, rather than the original worm drive - was this for reasons of backlash in the worm arrangement and rack, or some other reason?

Cheers,

Youra.

Hi Youra.
The external depth stop was the first thing that i got rid of ,a completely
useless part ,as you are probably aware the down feed index dial reads
in units that are nothing to do with reality so a digital readout is a must for
one of these machines.
The cnc drive attaches to the existing holes that are in the quill from the
the depth stop part ,the head has to be removed to rebore the top and bottom
lugs of the depth stop to suit the ball bearings for the lead screw.
As can be seen from the photo the lead screw is 7/16 x 10 TPI and has an anti
backlash nut. The connection for the nut has a split clamp that mounts on a
horizontal dovetail that connects to the quill ,to engage the nut the two halves
are located around the nut and clamp with 2 m4 screws.The stepper motor
sits within the original profile of the head ,as the machine is part manual with
cnc the head can be used over at 90 deg and still get down close to the table
if needed.
I did consider trying to improve on the rather poor down feed problems
associated with this machine but never use now the down feed handle for boring
type applications .The machine has been in this part cnc state for about 14 years
just using the Z axis for such things is easy to fit the 2 clamp screws and a control
file to down feed and return to a set depth is much easier than using the handle.
As can be seen in the second photo boring down in this blind hole is easy and the
zero backlash of this connection to the quill is worth having.

John

Edited By John Pace on 21/03/2020 20:24:27

Sticking quill?

Hi all.

Dave - no sadly - that would have been too simple - the quill resting on the table with the pinion removed goes up and down with the knee smoothly.

Bazyle - also unfortuneately not - actually remarkably clean in there! Cleaned and re-greased anyway though.

John - yes, the downfeed units make no sense - I also have a digital readout on the quill. I don't know if the depth stop is original or modified also (it's a 1mm pitch thread...) but it actually works reasonably well for my purposes - I get 0.03mm repeatability or so, according to the readout, in any case.

The quill rapid feed side of things is heavily modified with a whole new shaft, pinion (modified to 29 teeth), ball bearings at both ends and a new handle.

I've been able to adjust things to improve on the performance from the fine feed worm wheel, and I now only get unexpected movements of around 0.3mm, but I think with judicious use of the depth stop I should be able to live with that, and certainly not use the rapid feed for anything other than drilling (which feels lumpy, but will do). I might beef up the depth stop rapid movement arrangement though - I'm not sure they will last.

Long term a counterweight / gas strut and something like your arrangement based around the location of the depth stop seems very attractive - I'm a little limited in my ability to take the machine apart at the moment though...

Cheers,

Youra.

Hi,

I have a 1992 A1S which has the same or very similar vertical head.

I did not like the backlash or the garden gate type return spring. So I fitted two clock type coil spring that pull the quill upwards by the stop block. The springs rotate a shaft that pulls on some shim SS to pull the quill upwards. This removes the backlash and gives a lighter feel when drilling. I also have down feed for boring holes.

I'll try to post some pics to give you more idea.

Cheers

John

Edited By elanman on 24/03/2020 17:37:25

John,

Thanks for that - it does look a lot simpler to implement than the gas strut arrangement.

Something like one or two of these:
https://springcompany.com/products/constant-force-springs
would do perhaps... Perhaps I won't even need the extra shaft and SS shim in your setup..?

I'll take the machine apart again shortly to check the weight of the quill to work out what might fit - you don't perchance remember what the weight is (even approx...)?

Many thanks,

Youra.

Youra,

Thanks for the link, I've not seen those before.

Cheers

John

Hi all.

So - I make the weight of the quill around 8kgs - my final question really is - should I "counterbalance" with as close to that as possible, or do I want to bias noticeably above that, at say 12kgs or more?

I'll work out the best way to apply that shortly - I'm in the middle of some stuff just now, and don't want to loose the mill for a period just yet....

Thanks,

Youra.

Youra,

I did not use any calculations. I also have a Dore Westbury and so copied the idea from that. I made two as the quill is a lot larger than the DW. I do know that I made the springs twice as the first ones were not strong enough.

Sorry I'm not more help but it was a long time ago now.

Cheers

John

A few months along, and I thought I'd tidy this up in case anyone's still interested....

I decided on a weight counterbalance system, as I couldn't easily see how to get a gas strut into the space, and also wasn't too keen on the possibility that it suddenly fails. Springs were interesting, but again more challenging due to the space constraints.

I've adapted the existing quill guide block to carry a bar that's pulled up on each side by two 1mm stainless steel ropes that are tensioned by weights at the back of the machine.

The routing of the cables to the back is dealt with by a series of pulleys in a length of steel box section:

and finally there are ~8kgs of weights hanging on the end pulling on the cable. I printed a spacer bush to keep everything central and nicely symmetrical - much more material efficient than turning up something from the stock I had to hand:

(Some of the pictures were taken before the weights were attached, hence the cables are slack)

So far, it's doing really well - I'm confident that the cable strength is sufficient for the application - each cable only carries around 5kgs, and the manufacturers tell me that even with de-rating, each 1mm cable is comfortably rated at 25kgs. I've used the largest hardware (M5 mostly in pairs) that I could comfortably fit in, so in theory at least nothing is close to breaking.

Finished a week or so ago, I think it's doing the job I might add some more weight to make the upwards force a little more positive, but the backlash and lumpiness is largely gone!

Oh - and I also forgot to say that I've removed the spring that was biasing the pinion upwards...