Engine Cylinder Boring tips?

I've tried not to be long winded here just wanted to describe what was
going on before I asked the next best remedy, any and all suggestions
will be gladly accepted.thanks for bearing with this.
I am interested in adding some new business to my shop doing small
engine cylinder boring and honeing as there are a lot of cycle and lawn
shops waiting up to two weeks to have them done since the local machine
shop only does small cylinders when they have enough to fill a days
worth of work. I am familiar with the engine related aspects of
clearances and measuring. I don't have experience machining cast iron
liners though and know not to bother with nikasil ones. I have an enco
13" gap bed lathe and enco mill with 5" quill plunge with r8 shank
10x54 on the table. Chatter marks and varying spirals are what I get
with either machine. I have used an offset boring head in the mill with
both brazed carbides and hss tool inserted and locked through type bar.
On the lathe I have bolted to faceplate and bored with hss through bar
type boring bar with about the same results.
Even taking a light cut at 1 thou on the radius per cut still had light
patterns requiring about 6 thou on the diameter worh of honing to make
marks realy dissapear.
Both of these though are with bars atleast 5 inches long on the junk
cylinder I was test cutting and only supported on the tool holding end.
I am guessing this springing is what is giving the patterns?
It was suggested I use the lathe and make a bar supported at both ends
with the cutter passing through the cylinder mounted to the crossslide.
This seemed like a better idea being supported at both ends, but would
need to be about 18 to 24" long since it would need to be twice the
overall height/length of the workpiece for the cutter to pass through.
Had thought of using an angle plate with a hole bored through the center
would make it easy to hold the work and easy to get perpindicular to
the ways and only slightly difficult to center them once the faceplate
was squared.
Would this give me enough support using say a 1.25 bar since some of the
cylinders I would do are as small as 1.5 in maybe less?
Is overall machine rigidiy a problem ? I have been told the asain
machines and r8 shank just arent sturdy enough. True?
I have also had my eye out for a 16 " southbend since another job I have
been doing tapers on would go much nicer on it... if the supported
boring bar is a better option just needing a sturdier tool.
Or should I just come off the change and get a van norman or kwik way
bar and be done with it? This also becomes a prob b/c van norman 944
doesn't go small enough, kwik way bars look like I would need both a
fws2 and an fr model to cover the range I guess to see.
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I bored blocks for a few years with a Sunnen ridgid hone. It is an approved method from B&S and Tecumseh. I used AN100 stones for roughing cast iron blocks, finished with AN 500. With aluminum bores I used AN100 all the way. Sunnens honing oil is a must also. I built a machine to hold the hone and drill motor and pumped oil into the bore constantly while boring. I even bored a couple of small block chevys this way too. A hone and stones will set you back $300 or so, then you will need a hellatious drill to turn it. A T handle Milwuakee drill for around $200 works great. Greg
Reply to
Greg O
Check into a kennametal twin bore boring bar, they cut on both sides of the bore at the same time and will solve most chatter problems since the cutting head does not flex as the tool is feed into the hole being bored. They use carbide inserts and are adjustable just like a regular boring head. I have bored holes up to 24" depth and 3.5" Dia. with no chatter or tapering in the bore useing a lathe and these boring tools. I picked some up on ebay a few years back at a good price so you might want to do a search on kennametal and check if there are any available, you won't be sorry you if you buy some.
Best Regards Tom.
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I haven't bored engine cylinders, but I have done some pretty fine boring of guide holes for mold halves and some other parts. I originally had a small mill with B&S #7 spindle, and the best setup I could come up with was a 1/2" straight shank arbor in a collet. It was pitiful, I couldn't even bore Plexiglas without chatter.
I later upgraded to a J-head Bridgeport, and got the direct R-8 to boring head arbor. Otherwise all equipment was the same. I was then able to bore tool steel with ease, and have never had chatter again. If you are using a small straight shank instead of a direct R-8 arbor, get a new arbor. The enhanced stiffness will amaze you!
Reply to
Jon Elson
Mike, Your problem is stiffness with your machines and your tools. Any changes that increase the stiffness will help dissipate your problem. The tool of choice is a steam chest boring machine, but since few people own them anymore, I would do the following. Make a holding fixture that mounts to your face plate. It needs to allow a boring bar clearance gap between the cylinder bottom and the face plate and should be iron, not steel if possible. Steel amplifies vibration and iron dampens it. This will add considerable rotating mass. Second, you should modify your carriage, by removing the compound and making a dedicated boring bar holder that mounts in the compound mount. This holder should use the full width of the carriage to the greatest extent. Thirdly, you should use the largest diameter bar that the cylinder will allow and the widest clamp spacing that the new holder will allow. These changes will solve your problem and increase your throughput. Steve
Reply to
Steve Lusardi
I've always wondered why my small import boring head is so flexy and chattery when mounted in the milling machine's spindle. It's on a half inch stub arbor that goes into a collet. But I do have a variety of leftover 5C tooling stuff that could be converted into just such an item as you describe - thanks!
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Reply to
jim rozen
I do have an r8 arbor on the boring head. I think the lack of sturdiness there was the bar in the bottom of the offset head is only a half inch and had to be atleast 4~5 long under the boring head as the head itself was too laarge to enter the cylinder. Someone else mentioned using iron to dampen vibration, could this be part of my prob, I had previously fastened to the table with 1-2-3 blocks or ground parallels under the machinde flat areas of the cylinder.. Tried going faster with the carbide but that just made the marks closer together as the spring frequency increased.... I had best results with a fresh sharp tool steel bit with a sharp point but the feedrate moved down more than the tip radius could keep up with, when adding a small radius to the tip it got worse on the chattering, but the surface finish didn't have the torn edges like with the straight point. I fooled around several hours with my diamond hones with the tool point and edge... with no concrete results... I don't realy have a problem making tool edges work for my turning tools but then again they are atleast much shorter than the boring bar tools I mention here... then again I have no cast iron to turn the outside of to compare finish. THanks for help and any other suggestions that may come from the above.. thinking of making the larger diameter bar with it's own holder, however this wouldn't work for the lathe with cylinders ganged in threes and fours... should I consider finding a boring head for the mill that will use a larger extension bar? Most all of the ones I see in catalogs are the 1/2 tool holding inch variety.
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Keep in mind that you need to hone, using a Sunnen type box hone, at least a few thou. after boring. You may find that by leaving 5 thou, you can clean up the bore sufficiently to allow for some chatter in the boring stage. I use 80 grit stones to rough hone, and I can/have done 20 thou "overbores"just with the hone, so taking 5 thou out isn't going to be laborious. 10 thou takes about 15 minutes, hand honing, and you can get the bores round and straight that way.
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"Brian" wrote in news:mNOrb.102432$ snipped-for-privacy@nnrp1.uunet.ca:
A) Use the largest bar you can get in the bore. I've seen shops that bore cylinders use a boring head with follower wheels. This head has rollers the diameter to be bored, and feed into the cylinder behind the tool to stabilize it, much like putting a cutting tool on the end of a roll burnishing tool. The cutting insert is designed to flow the chips downward away from the rollers.
The other option, for a lathe, is a pneumatic actuated tailstock in the thru bore of the headstock, and a fixed, solid boring bar with center. Again, the larger the diameter, the more rigid and less chatter.
As a side note, make sure you use the factory register (DATUM) surfaces on that block for clamping/registering the part. Use of other surfaces, especially on small engines, will deform the block when clamped.
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Thank you on the hone suggestion also. Just for the overall efficiency I was wanting the best finish to begin with so going .010 over won't be a problem for cut or finish hone. I just don't want the embarrasment of a spoiled job.. I had a junk cylinder practicing the finish I could get now and using a hone to see how much was needed b't cuts to remove marks. Overall I would ldealy like to do this job on the mill since the coaxial indicator will give me a quick center over each hole.. mounting is quick and easy to make certain the cylinder is square to the table Considering a larger offset boring head that uses 1 inch bars... keeping my eye out for a kennametal or carbaloy similar twin insert cutter at anothers suggestion. The 1 in offset head came with r8 shank for a reasonable price.. hoping maybe the jump from a 1/2 in to a 1 inch bar will be where the sturdiness is being lost. Thanks to all who have responded.
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