Mods: Buck 6-Jaw Chuck
I've always been enamored
of 6-jaw chucks. If nothing else, they
are things of great mechanical beauty. I notice that many machinist's
I have a lot of respect for prefer them to the average 3-jaw for fine
work, for example 5Bears and the Machine Shop Trade Secrets book. In fact,
if you go through the latter, there is hardly a picture to be found of
a 3-jaw--it's all 4-jaws and 6-jaws. There is no surprise when you consider
the advantages of a 6-jaw chuck. Given
all that, it wasn't long before I went hunting for and found a high quality
6-jaw chuck on eBay. Mine is a 5" Buck Chuck with the fancy set-tru
capability. Having purchased this little beauty at an enormous discount
from full retail, my next chore would be to machine a backplate so I can
fit it to my Lathemaster. This will be my first project that had to come
together with any degree of precision.
Follow along while I plan
and execute this project.
The Spindle Nose...
My main concern is that
the chuck be accurate on the lathe. It is an expensive chuck, particularly
with the set-tru capability, and I want to realize its full potential.
With that in mind, the first order of business is to machine the interface
with the chuck spindle. If we do that, we can actually mount the adapter
to the spindle and carry out the remaining machining operations from there,
thus ensuring maximum accuracy (I think).
Getting the spindle interface
right is a matter of getting 3 mounting bolts positioned exactly correctly
as well as boring the proper hole for the spindle nose. This spindle nose
measurements are thus:
and most important fit is with the spindle nose 2.046" diameter to
a corresponding hole in the back plate. The 0.8235" spacer holes
are a less tight fit, but we are placing them using a bolt circle, which
is a calculated layout. I'll be double and triple checking it to make
sure I get that bolt circle right!
On the other
side of the adapter plate is the interface for the Buck 6-Jaw chuck. In
this case, we have 6 evenly spaced bolt holes for bolts that will hold
the adapter plate to the chuck, together with a hole in the chuck that
accepts a nose on the adapter. This hole is where the set-tru feature
comes into play. Within the hole are 4 Allen head adjustment screws that
enable the chuck to be moved radially versus the axis in order to get
it exactly aligned to the spindle's axis. Dimensions for the Buck chuck
look something like this:
There is some
good news here. For example, the spindle nose diameter (2.046") is
smaller than the set-tru hole (2.74"). This means that the hole needed
for the spindle hole can ride comfortable as a bore inside the nose that
mates with the chuck.
Here is a Rhino
3D model I made immediately after I got Rhino. This was after I'd already
made the backplate:
3-View "Ghosted" Solid Model of the Chuck
I purchased a couple of
cast iron round pieces from www.metalexpress.com.
A lot of materials would work, but the cast iron is pretty easy to machine,
and is often used in machine parts where a hardened piece isn't neccessary.
I bought 2 pieces that were 2" thick by 6" diameter. This is
pretty large, but I have another lathe chuck I also need to make a backplate
for that is a 6", and they didn't have much between 5" and 6".
We'll see how painful it is to rough out so much material. Given the mess
involved with machining cast iron, I would be tempted to go mild steel
the next time around. A piece of 12L14 would be much easier!
Combination Square with Center Head
TiN-Coated Drill Bits
Dividers, Outside Calipers, and Oddleg (Hermaphrodite) Calipers
Dial & Digital Calipers
Several Lathe Tools from
Glanze 5/16" Indexable Carbide and 1/4" Brazed Carbide Sets
3 and 4-Jaw Lathe Chucks
Telescoping ID Gages
Letter and Number Stamps
Granite Surface Plate
Tailstock Drill Chuck
Tailstock Die Holder
Dichropan T-4 Cold Bluing
the Adapter Plate
I'll tell you right now
that the way I did this was wrong in several ways. What follows is what
I actually did, so you can observe first hand the confused thought processes
of a novice. It just goes to show how important it is to really plan the
job ahead of time and not just meander around doing what pleases you.
At least that's true if you care about proficiency at all. I must say
that I still had a heck of a good time with it and learned a lot from
Boring the Off-Center
Chuck Mounting Holes:
Being a bit daunted
by how to hold my big chuck of cast iron in the lathe, I decided
to start out boring the off-center holes on my drill press. Later,
discovered this decision was a bad one, but not catastrophically
so. The problem is that the cast iron blank I started with turned
out not to be flat on the ends. This ensured that the holes drilled
were not exactly parallel to the axis, and so they didn't line up
quite right. The solution: enlarge then enough to provide clearance
and make a mental note. It seems like the right way to begin any
project is by squaring the workpiece!
There are 6-holes
on a 2.22" radius bolt circle needed for the chuck mounting
mark out these circles apply Dykem to one side of the cast iron
workpiece. This gives you a nice colored surface that will make
it easier to see your scribed layout lines.
Next, I marked out
the center of the workpiece using my combination square with the
centering head. I simply scribed two lines through the center at
roughly right angles using my carbide scriber. Using a center punch
and a light tap with a ball peen hammer, I made sure there was an
accurately positioned center dimple that my divider point could
Having located the
center, I scribed the bolt circle using a pair of dividers. The
radius on the dividers was set using my dial calipers. Once I had
a bolt circle, I center punched a point on the circle to be the
center of one of the 6 chuck mounting bolt holes. I then took the
dividers, and set them to the distance between bolt centers. This
can be calculated by the following formula:
Bolt Distance = Diameter * Sin(
360/(2 * Number of Bolt Holes))
In order to check
my math, I did a dry run around the bolt circle. I set the divider
leg in the first center-punched bolt center, put the other leg onto
the circle, pivoted the first leg to the next stop on the circle,
and so on. Each leg set down is a potential bolt center. If you
have all the distances right, you can walk all the way around the
circle, touching down once on each bolt center, and wind up exactly
back at the original center punched bolt center.
If all is well with
your math and measurements, go ahead and do the walk around with
the dividers once more, only this time, scribe a little arc across
the bolt circle at each stop. The intersection of the arc and the
bolt circle becomes the center point for the bolt. Center punch
each one of these. Okay,
we have now marked out the 6 hole circle for the chuck side of the
backplate. Next step was to scribe the circle that will be the OD
of the adapter snout that must fit into the set-tru cavity on the
Having completed the
layout work on one side, I then carried the cast iron blank over
to the drill press, and center drilled each of the center punched
dimples, including the center. Having done the center punching,
I got out my drill bit set and proceeded to bore a 0.274" ID
hole (or thereabouts, I just trial fitted the shaft of the bits
into the chuck until I got a good fit) in each of the 6 spots as
well as the center. I wanted the center hold to align to when laying
out the other side, to ensure everything stays concentric.
Boring the cast iron
went pretty quickly. I used Tap Magic as a coolant and lubricant,
kept my chip brush handy, and backed the bit out of the bore frequently
to clear chips. Eventually 7 holes were bored. As a check, I got
out my transfer punches, dropped one into place through the chuck
mounting bolt hole and into the adapter hole. I next checked whether
the other 5 holes lined up with the chuck using my trusty drill
bit. Everything was pretty darned close: I could get 5 of the 6
holes perfectly, with the 6th being not quite spot on. I believe
if I increase the ID of all of these holes slightly, life will be
good. We don't need perfectly tight holes because we're going to
use the set-tru feature of the chuck anyway. I later decided the
problem with the hole was that I didn't square the piece before
layout and boring.
Turn, Face, and
Make A Spigot for the Chuck to Grip:
I couldn't procrastinate
forever before mounting this thing in the lathe. In fact, I shouldn't
have procrastinated at all. This piece was about 6 inches in diameter--way
too big for my chucks. I therefore had to improvise another mechanism
to hold the cast iron in order to work on it. I opted for Steve
Bedair's method of drilling a center hole for a large bolt and
then holding the bolt in the lathe. I decided to get a little bit
fancy, hoping to increase precision, and finished a shaft to fit
fairly snugly, with a threaded hole in the shaft I could use to
tighten down a bolt and washer. In the end, I think a plain bolt
would have been just as good, but it seemed worth a try at the time.
Here's what it looked like with the sleeve held in the chuck:
Whoa! Check the clearance, Clarence!
are a couple of things to note about this picture having to do with
clearances. I quickly found out that machining this blank was really
at the limits of the lathe's capabilities in many ways. First, the
carriage would barely fit under. In fact, I had to stick the tool
way out over the edge and turn it down a bit to get there, working
a little at a time in several passes to take off about 3/16"
before I could just get under. Second, my nifty Quick
Change Tool Post absolutely wouldn't clear no matter what I
did. The turret post that came with the lathe gives a little better
clearance. Don't throw it out when you get your QCTP on! Many, I'm
sure, would have made up a plinth toolpost arrangement to deal with
this problem. The last problem was chatter. Mounting the cast iron
on that sleeve left way too much flex in the system. I wanted to
use a much larger bolt, but boring a decent sized hole in my drill
press just wasn't working out, so I forged ahead. I don't know how
much better a bigger bolt (say 3/4") would have faired, but
"It couldn't hoit!"
with the chatter, I was able to cut 20 thousandths with each pass.
I recently read an article about a guy with a Southbend who was
trying to do something similar and claimed it was absolutely impossible
to cut more than 3 thousandths on each pass. Not too bad when an
Asian lathe surpasses the might Southbend! With that said, I have
to assume the guy was either doing something wrong or his Southbend
was worn out and full of slop. Probably the latter. I stick by my
decision that I was better
off with new Asian machines rather than trying to rebuild old classics.
see all the nasty gritty dust and graphite cast iron throws off.
It does, however, cut pretty easily. When I get done with this piece
I'm going over the lathe again just like when I unpacked it to make
sure I get all that stuff out of the innards.
Turning down the spigot...
shot, you can see the other side, as well as the spigot I'm starting
to produce. Note the nasty chatter marks on the turned piece! It
took me quite a while to turn this down far enough that I could
take it off the sleeve, flip it around, and clamp it in the chuck.
It was worth the wait:
Nasty chatter marks on left, smooth finish
still see those horrendous chatter marks on the spigot, but check
the turned surface for a comparison. With the piece flipped around
and properly mounted in the 4-jaw, life suddenly got a lot better.
The chatter went away, the finish improved dramatically, and I could
crank up the spindle speed to really let my carbide tools sing.
At this stage, I still have a lot of material to take off both turning
and facing, but it's a whole lot more comfortable doing it.
Make a Spindle
This just makes it
easier to accurately measure the hole you will bore for the spindle
nose. It's very quick to turn such a gage to size, and it will be
useful for other projects. I turned mine with a shoulder in case
I want to later produce a full spindle replica (useful when mounting
your chucks to other tooling). I also used my number and stamp set
to mark it's dimensions and purpose on the back. This was easy to
do, using masking tape as a baseline to line up the text, and made
the whole thing look a bit more professional. I'll still be able
to read that stamped text long after tape or ink would have been
worn off and lost.
This gage should be
the first thing you make, BTW, under ideal circumstances. I stopped
in the middle, before boring the spindle hole.
Once having turned
and faced to reasonable dimensions, I bored the 2.046" ID spindle
nose hole to a depth 1.25". This is probably more than I need
depth-wise, but I'd rather have too much than too little. Make
a last facing cut on the spindle spacing side to achieve a fine
finish that's nice and flat.
Chuck Facing Side:
Now that the cast
iron blank is of more reasonable size, i.e. 5" OD, I was able
to flip it around so the chuck side was exposed and place it in
I'll turn down the nose to get to the right
length rather than facing it down...
Turn the shoulder
that will fit inside the chuck to 2.74" OD by 0.5" deep.
part that goes inside the chuck. When looking to get to the proper
depth for the spigot, as well as the overall length of the backplate,
I had to remove quite a lot of material. I remembered the adage
learned from Machine Shop Trade Secrets: remove that material by
turning, not facing, it goes much faster. He was right too! This
is especially so for a cheap Asian lathe that lacks a power cross
feed. When facing you can use the leadscrew feed. The downside is
you build up an irregular shoulder that will have to be properly
faced, so be sure to take that into account on your planning for
how much material to remove.
Face the shoulder
that goes against the chuck. I did this facing operation before
my final turning on the spigot that goes into the chuck. The latter
I undercut a little deeper than the shoulder so it would all fit
cleanly and squarely.
Trial fit the chuck
over the back plate nose before removing the back plate from the
Making the 3 spacers:
Before beginning to
make these three spacers, I realized I was going to need a tailstock
die holder for threading. The threads really need to be lined
up straight as these pieces need to fit true to ensure proper alignment.
So, you may want to take a brief detour over to the tailstock
die holder page if you don't already have one of your own. It's
an easy project and very handy once you are done.
Place some round steel
stock at least 0.8" or greater in diameter in the 3-jaw chuck.
I used an 8" length. I'm cutting a pretty long length, so I'll
turn with the live center.
Center drill and install
live center. I wound up using my cut-off tool to create the edges
of the spacer--it made them nice and flat as well as providing the
necessary clearance for me to go in and turn down the threaded areas
to the proper OD.
Using the cut-off tool to groove next to the
spacer bodies (colored in Black with a Sharpie)...
Now I'm turning down the threaded areas to
proper OD. I used a 1/4" carbide insert tool for this--there
wasn't room for my normal Glanze 5/16" indexable tools! I also
had to cut two passes with the cut-off tool to gain enough room
to work in. Finally, that cut-off groove also provided a relief
groove inboard of the threads.
the proper OD's are turned on the shaft, you can remove it from
the lathe and use the vertical bandsaw to cut apart the pieces.
I made four even though I only needed three. It only takes a little
longer and you have a spare if things go wrong.
Spacer blanks cut apart with the vertical
bandsaw. Note the clearance grooves where the threading can stop...
put each one back in the lathe, fired up my new tailstock die holder,
and cut the threads. Along the way I also used a well-chalked file
to finely bevel any sharp edges before threading.
It's a bit groady looking with this much magnification.
The whole thing is about 1" long.
last fit of ornamentation, I decided to try out a little cold bluing
Dicropan T-4 and Oxpho-Blue Creme were both tried) to put a
finish on the little buggers. The original spacers that came with
the lathe have some sort of a black oxide finish on them too. I
have to say, I like the effect. People complain that cold bluing
looks lousy on guns, but for parts it beats an unfinished state
and is really easy to do!
Blank, original that came with the lathe,
and my freshly cold blued part. I like my finish better, although
the threads look lousy!
On the originals there
is a 5/8" flat milled for a wrench, but they seem to work fine
finger tight, so I did not provide the wrench flats. If it gets
too annoying I may Loctite the spacers in. In fact, I am tempted
to do that on the originals too.
We're almost done!
Bolt circle for spacers marked out with Dykem...
Mark out the bolt
circle for the spacers. Since I had already bored the spindle nose
hole, I my oddleg (hermaphrodite) calipers to mark out the circle.
I then eyeballed the right between hole spacing on a finished backplate
using a pair of dividers. Walk the dividers around the bolt circle
on the new backplate. You'll see whether they are too wide or too
narrow--dividers that adjust with a threaded fitting are handy here.
Remember that the circle magnifies the error since you go around
once for each bolt. When you get to where you can walk the dividers
all the way around the circle and end up exactly where you started,
you have the right distance and can now scribe the cross points
to drill. There are also math formulas to calculate the distance,
but this was quick and easy for me.
Preparing to Tap with Piloted Tap Wrench (Enco
Drill the holes for
the threaded spacers. Tap them. Assemble the chuck and backplate
and trial fit to the spindle. The last step for me was to counterbore
the 6 chuck bolt holes so that the bolt heads and nuts would be
The chuck installed together with the first trial
piece turned. Runout adjust easily to 0.001" with Set-Tru!
This is an experienced chuck--some dings!
It is a beauty though, no?
When all was
said and done, was it worth it? I have to say it was a worthwhile project
for me. I got the chuck on eBay for $240, which is much less than the
new cost for the chuck. In addition, it was good experience to make the
backplate. I have to say that the feel of this chuck is far superior to
the Asian chucks that came with the machine. The key is silky smooth,
with virtually no trace of backlash.
I Encountered, Things I Learned...
- My method of using a bolt
to hold the initial blank until I could machine a spigot a chuck could
hold worked very poorly. There was tremendous chatter involved. I've seen
someone else center drill the bolt and bring a live center in to the equation.
That, and a much large bolt seem like must haves for the next go-round
with this. OTOH, I got through it without harming the lathe or myself
so maybe I shouldn't sweat it!
- It's hard to lay out precision
bolt circles by hand. The circle for the 3 spacers was off on 1 spacer
by 5 thousandths. It was that much closer to center than the other 2 holes.
I fixed it by turning down that spacer to a slightly smaller diameter.
In future I'd like to find a way to lay these out more precisely.
- I drilled my 6 holes for
the chuck without first facing the ends of the cast iron blank. Those
ends were not square to the sides so neither were the holes. I made them
slightly oversized and it all worked out fine. They're just clearance
holes. I would have been in a world of hurt had precision mattered here.
- Cast iron is pretty tough
to machine! I would be tempted to use 12L14 the next time. Looks like
I will get the chance as I need to make backplates for 2 more chucks.
- I am suspicious of the
accuracy of my cheap Asian drill press. Eventually, I will own a mill
which will be much more accurate. Also, I drilled using a big vise, but
a clamping kit would have been helpful as well.
- When I first inserted
the spacers in their holes, it looked like the threads were cocked. This
was disappointing since I had used a piloted tap wrench to get them straight
in the first place. It turned out that the threaded inserts were just
too long. I used a tapered tap to thread the holes and the tapered end
needs a lot of hole depth to start making threads. I solved the problem
by facing some of the threads off on the lathe, doing so with a nut in
place so that removing the nut would straighten out any damage I did to
the threads. A better answer would be to use a bottoming tap and thread
the hole all the way to the bottom.
- Initially, one of the
three nuts would not go through the spindle hole--I had to remove the
nut mount the chuck, and put the nut on from the other side. I had assumed
this was due to some of the other precision problems, but this turned
out not to be the case. I tried to put a wrench on it, and while this
nut was identical to the others thread-wise, it required a significantly
larger nut! My brother-in-law says that my mistake was in assume to quickly
I was the one with the precision problem rather than the nut factory.
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