Re: Quill backlash
Posted by
Dan Mauch
on 1999-07-30 13:11:38 UTC
On my knee mill I raise the knee so there is no backlash.
On my mill drill I has .02 backlash. Here issomething I wrote up.
Solving the mill drill quill backlash problems
I traded for a new Mill Drill and thought that it could fill a need in my
home shop.
Even though I have a full size knee mill and a floor drill press, I could
see where it would
be a nice addition. I also wanted to add a CNC system for automated
manufacturing of
certain parts. Sadly, I found out the following.
1. The X axis had .017 backlash and the acme lead screw pitch was off by
.001 per inch.
2. The Y axis had .016 backlash and the acme lead screw pitch was off by
.001 per inch.
3. The Z axis had .020 backlash.
4. The X axis table to saddle dovetail had a bind in one location.
This makes retrofitting the mill drill to CNC a nasty idea. Even CNC can't
make silk out
of a sow's ear.
Undaunted, I decided to fix the problems.
First, I fixed the tight spot on the X axis by lapping the table to the
saddle using a special
non embedding compound. Next, I replaced the X and Y axis acme lead screws
with
5/8" .200 pitch (5TPI) ball screws and ball nuts. Third I machined the end
plates for a
17MM radial bearing to reduce the side loads that would be imposed by a
timing belt
pulley attached to the new ball screws. This improved the accuracy and the
performance
immeasurably. Unfortunately, solving the backlash in the Quill was a lot
harder.
I have seen where a lot of folks got around the problem by adding a ball
screw to drive
the quill up and down for CNC applications. I started to build several
versions of this
approach and figured that it was going to be to hard to relocate in the
average home shop.
Additionally it doesn't solve the problem . it gets around the problem. So
after spending
$100 on material, I dropped the standard approach and decided perhaps that
solving the
problem was a simpler better way to be able to add CNC.
The current fine feed mechanism had less than .001 backlash between the
pinion shaft
worm and worm wheel. So I took the pinion shaft out to see if I could figure
out why
there was so much backlash in the pinion to quill rack. It is virtually
impossible to
measure anything while it is assembled. What I determined is that the rack
and pinion
were properly machined and are made to close tolerances. However, the
centerline of the
pinion shaft relative to the rack is off quite a bit ergo the excessive
backlash. Accordingly
the solution would require build up of the power head frame and re-boring it
correctly.
This was out of the question for many reasons. Thus it came upon me like a
thunderbolt
that if I would replace the existing end plate on the left side of the power
head with a
new end plate machined with the bore eccentric to the 1.418" hub in the end
pate this
would allow me to rotate the end plate for proper engagement of the pinion
with the rack.
It would also be necessary to make a similar end plate for the right hand
side of the power
head and to locate this under the worm wheel housing. Last the pinion shaft
journal
located on the right side of the power head would have to be re-machined
smaller so that
an eccentric end plate could be installed.
With this solution in mind I proceed to manufature parts using the existing
parts
as the guide for the modifications.
Disassembly.
1. Raise the quill all the way up and lock the quill in this position with
the manually
operated quill lock.
2. Loosen the quill retraction spring retaining knob/screw about 3/8 of an
inch.
3. With a glove on your hand rotate the retraction spring to get the lugs
on the spring
housing clear of the spit pins.
4. Pull the housing out and carefully let the retraction spring unwind.
5. Remove the spring housing retaining knob.
6. Remove the philips head screw holding the inside of the spring to the
pinion shaft.
Place these parts in a part box for latter re-assembly.
7. Unscrew the fine feed engagement knob/screw on the right hand side of the
power
head
8. Slide out the manual quill feed handle assembly being careful to catch
the spring
that is located inside the pinion shaft. Place these parts in a part box for
latter re-
assembly.
9. Locate and lift out the key from the key way. Place these parts in a part
box for latter
re-assembly.
10. Slide out the worm wheel. Place these parts in a part box for latter
re-assembly.
11. Remove the two allen cap screws holding the fine feed and worm
housing. Place
these parts in a part box for latter re-assembly.
12. Slide the worm wheel housing off the pinion shaft. Place these parts in
a part box for
latter re-assembly.
13. Slide the pinion shaft out of the power head frame. Place these parts in
a part box for
latter re-assembly.
14. Remove the end plate also called the spring base by removing the three
retaining
screws. Place these parts in a part box for latter re-assembly.
This sounds like quite a dismantling process but will take longer to read
than to
accomplish. It is really quite easy to do.
Measurements.
Measure the diameter of the pinion shaft at two locations.
1. Where the pinion shaft penetrates the end plate on the left hand side of
the power
head. The shaft should measure .7083 +/- 0.0002"
2. Where the pinion shaft journal lines up with the pinion shaft bore on the
right hand
side of the power head frame. This should measure 1.417 to 1.418"
3. Where the power head bore on the right hand side of the frame is. It
should measure
1.4188-1.419
4. Where the end cap hub matches up with the bore on the left side of the
power head.
This should also be 1.4188-1.419
If your parts match these dimensions then your machine can be retorfitted
with the
eccentric end plates very easily.
Send your pinion shaft your pinion shaft to me if you don't have a lathe. If
you do chuck
up the pinion shaft in your lathe. Use a live center for the other end. Make
sure that the
shaft turns true to within .001 TIR.
1. Machine the journal that was 1.418diameter down to 1.150" +.000/-.0002.
with a 125
finish or better. This steel is tough so take it easy.
2. Install the left side end plate into the power head with the low spot
center punch
mark all the way at the back of the bore away from the quill. This will
initially give
maximum clearance.
3. Install the right side end plate into the power head with the low spot
center punch
mark all the way at the back of the bore away from the quill. This will
initially give
maximum clearance.
4. With the quill manual lock in the locked position rotate both end plates
until you
have no play when you rotate the pinion shaft by hand. Scribe the slots onto
the right
hand end cap to the power head.
5. Remove the right side end cap and drill and tap the power head frame
for a 10/24
thread choosing a location that will not bury the drill bit into the quill.
The location
away from the quill on the side toward the motor should be good.
6. Reinstall the right side end plate and readjust for zero backlash without
binding the
pinion gear with the quill rack
7. Install and tighten the left and right side end caps. The left side end
plate matching
threaded hole in my machine were not properly located at the factory. They
drilled
them by hand! So you may have to drill a new hole to match up with the
slotted holes
in the end pates provided.
8. Reinstalled the fine feed worm wheel housing leaving the mounting screws
loose.
9. Reinstall the worm wheel engaging the worm with the worm wheel.
10. Reinstall the shaft key, spring and handle assembly.
11. Reinstall the handle engagement knob.
12. Reinstall the quill retraction spring and philips screw.
13. Reinstall ad adjust the retraction spring for proper tension. Tighten
the spring retaing
knob/screw.
14. Adjust the location of the worm wheel hosing so that it has minimum
backlash with
the worm wheel.
15. Unlock the quill's manual lock and check for proper operation. The quill
should now
have <.005 backlash and will probably be around .002" Adjust the end plates
if there
is any binding.
16. Adjust the worm wheel housing if necessary to freely rotate the fine
feed shaft and to
remove any work to worm wheel backlash.
Happy Mill Drill Quill
Dan
On my mill drill I has .02 backlash. Here issomething I wrote up.
Solving the mill drill quill backlash problems
I traded for a new Mill Drill and thought that it could fill a need in my
home shop.
Even though I have a full size knee mill and a floor drill press, I could
see where it would
be a nice addition. I also wanted to add a CNC system for automated
manufacturing of
certain parts. Sadly, I found out the following.
1. The X axis had .017 backlash and the acme lead screw pitch was off by
.001 per inch.
2. The Y axis had .016 backlash and the acme lead screw pitch was off by
.001 per inch.
3. The Z axis had .020 backlash.
4. The X axis table to saddle dovetail had a bind in one location.
This makes retrofitting the mill drill to CNC a nasty idea. Even CNC can't
make silk out
of a sow's ear.
Undaunted, I decided to fix the problems.
First, I fixed the tight spot on the X axis by lapping the table to the
saddle using a special
non embedding compound. Next, I replaced the X and Y axis acme lead screws
with
5/8" .200 pitch (5TPI) ball screws and ball nuts. Third I machined the end
plates for a
17MM radial bearing to reduce the side loads that would be imposed by a
timing belt
pulley attached to the new ball screws. This improved the accuracy and the
performance
immeasurably. Unfortunately, solving the backlash in the Quill was a lot
harder.
I have seen where a lot of folks got around the problem by adding a ball
screw to drive
the quill up and down for CNC applications. I started to build several
versions of this
approach and figured that it was going to be to hard to relocate in the
average home shop.
Additionally it doesn't solve the problem . it gets around the problem. So
after spending
$100 on material, I dropped the standard approach and decided perhaps that
solving the
problem was a simpler better way to be able to add CNC.
The current fine feed mechanism had less than .001 backlash between the
pinion shaft
worm and worm wheel. So I took the pinion shaft out to see if I could figure
out why
there was so much backlash in the pinion to quill rack. It is virtually
impossible to
measure anything while it is assembled. What I determined is that the rack
and pinion
were properly machined and are made to close tolerances. However, the
centerline of the
pinion shaft relative to the rack is off quite a bit ergo the excessive
backlash. Accordingly
the solution would require build up of the power head frame and re-boring it
correctly.
This was out of the question for many reasons. Thus it came upon me like a
thunderbolt
that if I would replace the existing end plate on the left side of the power
head with a
new end plate machined with the bore eccentric to the 1.418" hub in the end
pate this
would allow me to rotate the end plate for proper engagement of the pinion
with the rack.
It would also be necessary to make a similar end plate for the right hand
side of the power
head and to locate this under the worm wheel housing. Last the pinion shaft
journal
located on the right side of the power head would have to be re-machined
smaller so that
an eccentric end plate could be installed.
With this solution in mind I proceed to manufature parts using the existing
parts
as the guide for the modifications.
Disassembly.
1. Raise the quill all the way up and lock the quill in this position with
the manually
operated quill lock.
2. Loosen the quill retraction spring retaining knob/screw about 3/8 of an
inch.
3. With a glove on your hand rotate the retraction spring to get the lugs
on the spring
housing clear of the spit pins.
4. Pull the housing out and carefully let the retraction spring unwind.
5. Remove the spring housing retaining knob.
6. Remove the philips head screw holding the inside of the spring to the
pinion shaft.
Place these parts in a part box for latter re-assembly.
7. Unscrew the fine feed engagement knob/screw on the right hand side of the
power
head
8. Slide out the manual quill feed handle assembly being careful to catch
the spring
that is located inside the pinion shaft. Place these parts in a part box for
latter re-
assembly.
9. Locate and lift out the key from the key way. Place these parts in a part
box for latter
re-assembly.
10. Slide out the worm wheel. Place these parts in a part box for latter
re-assembly.
11. Remove the two allen cap screws holding the fine feed and worm
housing. Place
these parts in a part box for latter re-assembly.
12. Slide the worm wheel housing off the pinion shaft. Place these parts in
a part box for
latter re-assembly.
13. Slide the pinion shaft out of the power head frame. Place these parts in
a part box for
latter re-assembly.
14. Remove the end plate also called the spring base by removing the three
retaining
screws. Place these parts in a part box for latter re-assembly.
This sounds like quite a dismantling process but will take longer to read
than to
accomplish. It is really quite easy to do.
Measurements.
Measure the diameter of the pinion shaft at two locations.
1. Where the pinion shaft penetrates the end plate on the left hand side of
the power
head. The shaft should measure .7083 +/- 0.0002"
2. Where the pinion shaft journal lines up with the pinion shaft bore on the
right hand
side of the power head frame. This should measure 1.417 to 1.418"
3. Where the power head bore on the right hand side of the frame is. It
should measure
1.4188-1.419
4. Where the end cap hub matches up with the bore on the left side of the
power head.
This should also be 1.4188-1.419
If your parts match these dimensions then your machine can be retorfitted
with the
eccentric end plates very easily.
Send your pinion shaft your pinion shaft to me if you don't have a lathe. If
you do chuck
up the pinion shaft in your lathe. Use a live center for the other end. Make
sure that the
shaft turns true to within .001 TIR.
1. Machine the journal that was 1.418diameter down to 1.150" +.000/-.0002.
with a 125
finish or better. This steel is tough so take it easy.
2. Install the left side end plate into the power head with the low spot
center punch
mark all the way at the back of the bore away from the quill. This will
initially give
maximum clearance.
3. Install the right side end plate into the power head with the low spot
center punch
mark all the way at the back of the bore away from the quill. This will
initially give
maximum clearance.
4. With the quill manual lock in the locked position rotate both end plates
until you
have no play when you rotate the pinion shaft by hand. Scribe the slots onto
the right
hand end cap to the power head.
5. Remove the right side end cap and drill and tap the power head frame
for a 10/24
thread choosing a location that will not bury the drill bit into the quill.
The location
away from the quill on the side toward the motor should be good.
6. Reinstall the right side end plate and readjust for zero backlash without
binding the
pinion gear with the quill rack
7. Install and tighten the left and right side end caps. The left side end
plate matching
threaded hole in my machine were not properly located at the factory. They
drilled
them by hand! So you may have to drill a new hole to match up with the
slotted holes
in the end pates provided.
8. Reinstalled the fine feed worm wheel housing leaving the mounting screws
loose.
9. Reinstall the worm wheel engaging the worm with the worm wheel.
10. Reinstall the shaft key, spring and handle assembly.
11. Reinstall the handle engagement knob.
12. Reinstall the quill retraction spring and philips screw.
13. Reinstall ad adjust the retraction spring for proper tension. Tighten
the spring retaing
knob/screw.
14. Adjust the location of the worm wheel hosing so that it has minimum
backlash with
the worm wheel.
15. Unlock the quill's manual lock and check for proper operation. The quill
should now
have <.005 backlash and will probably be around .002" Adjust the end plates
if there
is any binding.
16. Adjust the worm wheel housing if necessary to freely rotate the fine
feed shaft and to
remove any work to worm wheel backlash.
Happy Mill Drill Quill
Dan
> On another subject, there has been a lot of discussion on ball screws,etc for the mill table. What are all you folks
>doing about the Z axis mechanism for your mills ???????
>
> Larry...............