Long small diameter boring
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  1. #1
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    Default Long small diameter boring

    I have a job that i run for another shop. Do perhaps 2 to 3 line bore jobs per year for a gentleman in So Calif that does almost
    exclusively 4 cam Porsche engine work.

    My part of the work is to make the case parting faces flat, make the cylinder barrel seating faces flat and parallel and bore the main housings to a
    size to give the correct crush on the roller bearings for the crank.

    Since the case half's get shortened some , the oil pump housing as well as the front and rear oil seal bores must also be trued to size.....
    and finally the "jack shaft" that drives the cam drives needs to be bored true and to size.

    For years i have struggled with this last part of the work....the cam drive shaft has an internal bore of 1.181" (+.0000 -.0003")
    The housing carries two bushings , one at the outside rear of the case (easy) and one that is almost 7" inside at its far end.....That is a pretty good reach.
    Further the case material (Aluminum/mag alloy) is somewhat abrasive and tends to kill tools.

    For sometime i have used a shop built bar and a brazed carbide tool in a square hole at the end of that bar....making size adjustments by touching the
    indicator to a fixed indicator and advancing the tool in its hole...securing via a clamping screw.....

    Small adjustments were at best tedious.

    Last week i splurged and bought the shop a present....Been watching e-bay for some time and when this came up, i jumped....

    Its something called "Silent Tools" and its made by Sandvik.....Its a long boring bar which is over 7 1/2" long.
    On the end it has a small slide that carries a small triangular insert.

    The slide is moved by a dial and screw that has graduations in .0004" increments on the diameter....Move increments are further sup divided by a vernier .
    The one i bought covers a range from about 20 mm up through 32mm if one employs the optional spacer shim on the tool insert holder....



    Here you can see the basic setup....Entire length of the bar is extended by the use of an adapter that steps the bar base coupling (Capto C3) up to my
    Cat 40 Capto adapter. (Capto C5 to Cat 40)

    Could have made the package shorter by purchasing a direct C-3 to Cat 40 coupling piece , but i was already tooled to go as shown , so i gave it a try....

    Here you can see the bar running at its full length, just completing the cut.



    This shot gives some idea of the size of the bar and the bore.....



    Here is a shot looking down through one of the cylinder bores into the case...the bar and inner bearing cap can be seen....



    More to follow............................

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  3. #2
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    Ross,

    I bow and scrape if you are able to get that to go with no chatter. That is a serious amount of overhang! Is there some internal vibration damping magic in that bar? What is the insert like? You mentioned abrasive material. Are you using a diamond-coated tip?

    Cheers!!

    RKlopp

  4. #3
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    Additional shot showing the bar working inside the case viewed from the front of the case through the oil pump housing bore....



    So the end result was that the bar preformed as advertised......I was able to control the size within specs and got a good finish on the
    bore ID...(no chatter)

    I was even able to hold size after changing the insert edge (stopped cutting when i was within .0005" of finished size.....

    Personally i am a big fan of the Sandvik inserts/tools and their "Capto" system. I have a good local distributor and things ordered are often delivered here by the next working day.....Which is
    a good thing here as jobs often crop up unannounced and need to be completed quickly (in order to keep a mechanic working)...

    I had looked at these bars years back, but had trouble justifying the initial cost of a new bar and settled on making my own. (less than ideal)
    Retail the price i was given on this tool of about $4000.00 for the bar alone with no inserts or shims. The E-bay offering was significantly less although still pricey!

    Up side is that i completed the work in about 1/2 the time needed for the same portion using the shop built tooling...
    That and holding size with better surface finish made this portion of the job almost pleasant.....

    In all nice tool, good performance...problem solved!
    Cheers Ross

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    Rich:

    Finish is good...no audible vibration and inspection by the naked eye looks good....
    Bar has internal "magic" to dampen vibration...not sure what is in there, but seems to work.
    Insert is uncoated (Sandvik H10) their aluminum grade insert...small Positive with chip breaking top geometry....
    TCGX 1.2-AL H10

    Did need to index the tool for the finish cut as it stopped cutting with .0005" to finish....Should have indexed the corner sooner, but did not show any problems
    till i tried to get the last 1/2 thou...Bit tedious picking up the cut with the new edge without going over....Worked out well....
    There are days you get lucky i guess...
    Cheers Ross

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    usually at 5 to 1 length to dia of boring bar it flexes alot
    .
    sometime RPM needs to be slower to control vibration and whipping that is boring bar can cut different dia at different speeds due to unbalanace
    .
    quite normal for optimum cutting range that is taking
    -.005 dia cut
    -.002 dia cut
    then final cut
    as many metals when trying to cut less than .001" dia change like .0005 they dont cut but rub and you keep adjusting til it finally bites cutting often dia more than expected
    .
    many boring bars with 2" or 3" extension, the extension is removed as they cut much better and more stable without the extra length

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    TomB:
    I am aware of the conditions affecting the bar and its performance. I was quite willing to buy the direct C-3 to Cat 40 Capto mount to shorten the bar if it had difficulty
    holding size and finish with the additional spacer/adapter...as ti turns out it worked just fine as shown...

    Have had good results with the Capto tooling running at extended reaches. This was my first exposure to their "anti vibration" boring tools...I am pleased with my results.
    Cheers Ross

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    Quote Originally Posted by AlfaGTA View Post
    TomB:
    I am aware of the conditions affecting the bar and its performance. I was quite willing to buy the direct C-3 to Cat 40 Capto mount to shorten the bar if it had difficulty
    holding size and finish with the additional spacer/adapter...as ti turns out it worked just fine as shown...

    Have had good results with the Capto tooling running at extended reaches. This was my first exposure to their "anti vibration" boring tools...I am pleased with my results.
    Cheers Ross
    .
    usually when i need a bore .0001 or .0002" bigger i rerun at higher rpm. often it will cut bigger as it deflects more from unbalanced load at higher rpm. i am not sure i would consider a balanced bar better as it would not so easily open bore .0001 or .0002"
    .
    as you adjust boring bar the cutter goes farther off center and the weight balance changes. i am not aware of any boring bar that is adjustable that stays balanced
    .
    some boring bars made from carbide instead of steel are inherently more rigid as carbide deflects less with the same deflection forces

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    Cool

    I had a horizontal job one time on my FP4NC, the set up was kind of tricky- complex featured part that was difficult to clamp and tram. Had to build a Capto c5 tool to reach the far end of a big casting. At 14" tool extension, tool runout measured .0002". I was surprised and very happy, saved me a lot of time. Great stuff.

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    Quote Originally Posted by AlfaGTA View Post
    Additional shot showing the bar working inside the case viewed from the front of the case through the oil pump housing bore....



    So the end result was that the bar preformed as advertised......I was able to control the size within specs and got a good finish on the
    bore ID...(no chatter)

    I was even able to hold size after changing the insert edge (stopped cutting when i was within .0005" of finished size.....

    Personally i am a big fan of the Sandvik inserts/tools and their "Capto" system. I have a good local distributor and things ordered are often delivered here by the next working day.....Which is
    a good thing here as jobs often crop up unannounced and need to be completed quickly (in order to keep a mechanic working)...

    I had looked at these bars years back, but had trouble justifying the initial cost of a new bar and settled on making my own. (less than ideal)
    Retail the price i was given on this tool of about $4000.00 for the bar alone with no inserts or shims. The E-bay offering was significantly less although still pricey!

    Up side is that i completed the work in about 1/2 the time needed for the same portion using the shop built tooling...
    That and holding size with better surface finish made this portion of the job almost pleasant.....

    In all nice tool, good performance...problem solved!
    Cheers Ross
    Anybody that can afford to have their 4 cam Porsche engine rebuilt can afford to spend some money on tooling.

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