Enco Boring Heads

" I have a job where I need to bore and sleeve aluminum transmission cases for a 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.

Jim

you might consider buying a cartridge from Komet or somebody and making the head. 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 milling machine.)

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.

Good Luck, DoN.

I have never seen this trick or heard of anyone attempting it.

How do you bore within .001" using a fly cutter?

Regards,

Robin

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 the cut.

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?

chuck

====================================== 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. George McD

--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

0.0001.

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! chuck

Nope.

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 repeatable results.

Regards,

Robin

--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 direction.

Harold

Me too, along with a fair amount of cursing (:

The key is to design the part such that these wee tolerances are not required.......

Regards,

Robin