My first post did not show up. Anyway, I need a boring head to complete
a job and don't have time to wait to buy one on E-Bay. I have a job
where I need to bore and sleeve aluminum transmission cases for a
countershaft and have to hold .0015 tolerance.
I have looked at Enco boring heads and they are scarily cheap. This
worries me and I wanted to see if anyone has bought and used one of
these Enco boring heads and if so what the results were. Were they
adequate and accurate? Any help will be greatly appreciated. Thanks,
" I have a job where I need to bore and sleeve aluminum transmission cases for
countershaft and have to hold .0015 tolerance."
Buy the enco, bore the holes, make the sleeves to fit the hole. Before
finishing off first bore, establish a constant by taking .002 off the diameter/
cut. A good toolmaker can make a flycutter bore within a thousanth.
The dial on them is one thou *radius* so if you move it one division
you get two thou on the diameter. However I've had good luck hitting
inside a thousanth by splitting the graduations on them, on the
smallest head they sell.
you might consider buying a cartridge from Komet or somebody and making the
we have made a few heads in the length and diameter we need for the job,
this allows us to use the micro adjust feature of the head without the cost
of multiple bars to do one off jobs
Yes it did. You just did not wait long enough for it to show
up. You are posting from google, and it takes a *long* time for
something posted from there to make it into its own reader. It will
apparently show up out in usenet in general before it will show up on
Google. If you want fairly quick feedback to assure you that the post
made it out -- find some *real* news server, not a web-based interface
to usenet news.
My experience with boring heads from Enco is limited to
boring/facing heads imported from France, and actually *made* by Gamet.
*Those* are excellent boring heads. However, they were sold by Enco
many years ago, (I used one bought new back around 1975 or so, and mine
was an eBay purchase several years ago with a 30-taper shank to fit my
I don't know *what* your "scary cheap" ones are like, as I have
not used them. This is why I did not bother to reply to your previous
posting, and I would not have replied to this one either, if it were not
for the problem with posting from google and not seeing what you have
posted. *Everyone* who posts from Google should not expect to see what
they post in any reasonably short period.
I have an Enco and a Criterion. They look identical. The Criterion
works far better in terms of being abe to adjust to within a thou.
However, if you do the sleeve trick someone else suggested, that isn't
an issue so the Enco should be OK. You might not hit exactly the dia
you want, but it should do a number of holes repeatably.
Generic information follows, basically outlines the method Ive used in the
past which seems to have provided me the best "luck".... many ways to skin a
cat, here's my way :
If a Criterion head is new or it has been left sitting for any length of
time, its best to completly dis-assemble it, re-assembling it with a film of
quality grease containing an EP additive on all moving surfaces.
Where there is 3 screws in the side, the two outer ones are to be set to
produce a definate drag and then they are not used or adjusted again in the
boring process, the center screw acting as a slide lock, basically, you do
not want any "stick slip" when the slide is adjusted.
Now, adjusting for size is done by unlocking the center screw, then backing
off the leadscrew to take out any backlash and then a bit more, after which
I reverse it again, coming back up to the new setting and again tightened
the lock screw........
Using this method, anyone should easily be able to consistantly obtain a
size within a very few tenths and without risking chatter or cutting
pressures moving the slide out of the desired position while the tool is in
I use a different technique. I position the boring bar such that advancing
the leadscrew pushs the bar out. This was there is no backlash. It
sounds like you are positioning the boring bar the opposite way?
Even a not so good one can do this. Two tricks, assuming you are using
the typical lathe boring bar as the fly cutter.
First, make sure that the tool is on or slightly below center. If you
are using the typical boring bar, the square hole for the tool bit is
on center so the cutting edge is above center by one-half of the tool
size. You will have to grind down or grind in considerable back rake
or hook. Side rake does not seem to be very significant as long as it
is not negative. For a good finish, you will need some nose radius but
hold to the minimum, as this will promote chatter. Be sure you have
adequate front and side clearance. Because the work moves closer to
the bottom of the tool in internal cutting, much more front clearance
is required than for an external lathe tool.
Second, you need a way to accurately adjust the tool bit. Drill to the
nearest size that you can that will provide adequate material for clean
up. Adjust the tool bit in the fly cutter to just touch the existing
bored hole, and make a pass. Carefully measure the hole, and adjust
the protrusion of the tool bit as required.
I tried micrometers and calipers with minimal success (not enough
hands). After reading Gingery, I drilled a 1/8 hole about 3/4 of an
inch up from the hole for the tool bit, and cross drilled for a set
screw. I used a thumbscrew for easy operation. (Gingery shows a clamp
around the outside of the bar) Took a short piece of 1/2 inch square
key stock and drilled and tapped for a 10-32 screw. Installed an
appropriate length screw, loctited it in the hole and cut the head off.
In operation, you put the screw in the key stock in the cross hole
over the tool bit and with a feeler gage space the key stock out the
appropriate amount from the end of the too bit, and tighten the thumb
screw. Loosen the clamp screw(s) for the tool bit and push it out
until it touches the key stock. Tighten the tool bit clamp screws;
remove the thumbscrew and key stock. Bore hole. By setting the key
stock stop out using the 0.0015 feeler, and the using the 0.001 feeler
between the bit and stop is possible to take a 0.001 cut on the
diameter. (Use metric feeler gages for a metric tool :-) )
Be sure to feed the boring bar out/up as well as in/down to avoid swirl
marks in the bore. Because of the spring make several passes without
advancing the tool when you get close to the final size.
Only very light cuts should (can) be taken. A 0.010 cut is about max
in steel with a 1/2 inch bar in the typical home shop set-up, and most
likely you and your machine will be happier with 0.005. A short single
end boring bar will work better than the longer double end bar. Like
most traditional machining operations -- feel is everything.
--The day will come when you'll need to hold a tolerance of
*.0001"*. Buy the right tool first time and you'll never have to buy
another one. Criterion makes nice boring heads; I've had the 2" dia
body one for 30 yrs and the 3" dia one for maybe 20. Very nice.
I realize Criterion makes boring heads that are designed for borings
to tenths, but they are quite expensive, like damn near 1000 in J&L catalog.
I have a "normal" 2 inch criterion boring head and while it works very
well, I don't see how it could possible be adjusted to only take off
Seem to me that even if you have a tenths setting boring head, that
lots of things will affect the ability to achieve that level of accuracy.
Things like spindle runout, slop in the quill, and machine vibration
come to mind. Seems like a slow power down feed would be required too.
It also seems that moving into this accuracy requires some pretty
good measuring insturments too. My telescoping gages are not going to
"measure up" .
I have bored model engine cylinders and learned to lap them to
improve the roundness and reduce the taper.
And then again, maybe I need to be educated!
At final setting there is no backlash present.
Rather than continually pushing, I will release the tension, to
re-distribute the lube film on the screw and slide by first unlocking and
backing off the leadscrew *each* time an adjustment is made.....this being
same as the method we used to position jig bore tables, always unlocking
first then backing off the table enough to move it slightly in the opposite
direction before reversing to take out backlash and finally tramming back up
to your final setting........
Has worked very well for me is all--*especially* when on boring many holes
during the course of a day as temp changes and tool wear might make it
necessary to frequently adjust size either direction in order to make the
tool cut larger *as well as* smaller........
I'd agree with you.
Even grinding any feature to within .0001" is a delicate job, and at that
point (as you said) a lot of things become important. Unfortunately
temperature is one of them. Surface finish is another.
I would never rely on a boring head to get me within .0001", at least on a
manual mill. CNC mills and jig borers are different beasts all together.
And besides, I bet there are very few HSM applications where one would need
to rely on a boring head (to one or two tenths). In industry where
additional operations (like honing/lapping) can cost big bucks, boring heads
costing thousands of dollars are not uncommon. At that point, it becomes
cost effective to play with cutter geometry and feeds/speeds to obtain very
--Maybe a little exaggeration on my part but I *can* hold .0002"
with the non-super-precise model. It isn't needed all that often but when
it is I've got the tool for the job. On the one or two times I have had to
hold tighter tolerance I've tried to do the jobs with a lathe..
Working closely isn't the tools so much as the machinist running them. A
poor machinist with great tools often can't do the job, but I've seen
outstanding work come off poor machines at the hand of a good machinist.
That's what sorts them out in a heart beat.
Don't sell your telescoping gages short, Chuck. You'd be surprised how
closely you can work with them if you develop the proper feel. I've
trusted them to .0002" often, with good results.
Could be the general condition of your machine. You should be able to bore
cylinders and get them both round and straight. I'd be interested in
hearing how you've gone about boring your cylinders. Could be you're
missing something, unless you have a well beaten machine.
Lets talk about it and find out! Could be you need a little nudge in some