View Full Version : Help With Boring Bar

06-25-2011, 12:31 PM
I want to bore holes for larger cylinders on my VW hoddy on the vertical mill
with a 3 inch boring head.I can't understand the best option on the right
boringbar for the job.I want a 3/4 bar,about 4 inch long.The end cut needs to end at 90 degree's so the top of the cylinder seals properly.see the photos i found with examples of what i want to do.Any MSC etc part numbers would really help me out.Thanks!
another view on head thats been opened ....

06-25-2011, 03:14 PM
Lots of lookers but no advise.I was thinking these MSC part numbers but like to get some opinions of more experienced guys then me.
I just got this vertical milling machine and i'm a newbie at this stuff.
3/4 boring bar 78085826
blades 78639697
Help appreciated!

06-25-2011, 04:06 PM
Why don't you just do a search on enco or MSC?

Here is a carbide tip bar from Enco. try their search facilities you can select things by parameter.


You might also consider a carbide insert boring bar since it might be more useful in the long run, especially if you don't have a diamond grinder. You can also make a boring bar out of 3/4" cold rolled and a 0.250 or 0.375" piece of round High Speed Steel (HSS). Either set screw the HSS in place or braze it or clamp it. I made one and it works well for me.


06-25-2011, 04:18 PM
How about something like this: http://www.mesatool.com/index.php?main_page=product_info&cPath=1&products_id=5

06-25-2011, 04:46 PM
It looks like you are needing a boring and facing head. The boring part to make the hole and the facing part to do the flat surfaces.

06-25-2011, 04:47 PM
I do similar average 3 times per week for last twenty years.

One thing that would concern me is deflection of the actual tool, more so the last link above at 6" long.
The other first link may be too sort at 4 1/2" total length and will need the tip reprofiling. Have had great success with carbide on aluminium even though its far from recommended.

If intending to do the cylinder head like piccy, you will run in to problems. To get that may be easier overall to turn in lathe.
If using boring head to do that the bottom surface, it wont be smooth the only way to do it is to keep opening up the head little by little set on depth stop.

May have to bore out cylinder undersize and hone to size with those three prong type cutters.

06-25-2011, 06:03 PM
I was told by one guy who doe's this that he use's a Criterion 3/4 inch bar with TPGT 321A-2C cutters.Only one of those i see on MSC is a 8 inch and my knee don't go low enough to get the engine case under that.The case's i do are made out of magnesium and cut without coolant about 250-300 rpm and look like mirror finish.I am told on the aluminum heads to use coolant, tap magic or Relton A9 and go slow about 250 rpm so not to gall. I have searched MSC and Enco to death but being new to running a Milling Machine i
am having a hard time looking at everything.I used to have a wacky looking thing that actually bolts to the case and head and is used in a drill press but set up on this is a lot of work.The shops we send to in California use a Mill.
Shipping stuff from Texas is costly and time consuming so i want to do it myself.Also the cylinders can not be modified that have to used as is.
I have a huge pile of old case's and heads to practice on so i know it will be a learning process but whch tools has got me stumped.

06-25-2011, 06:16 PM
You can always get the 8 inch bar and cut it to the length you need.

06-25-2011, 06:16 PM
You would be better off with a smaller head and a boring bar coming out perpendicular to the spindle than having a long bar hanging off. Something like this will be a lot more rigid.


06-25-2011, 06:42 PM
Perhaps there is a little 'lost in translation' here...

There really are two questions at hand, in my opinion:
1) What boring bar/insert grade and type to use?
2) What method is used for such a boring procedure?

The first question is either the easiest or the hardest depending on how you approach it ;) For, just about any boring bar will get the job done. You could use a broached rod with a square HSS bit if you wanted. You could also use a solid carbide bar. In between there are inserts galore and a multitude of bars made to fit them.

The second question is more pressing. How to face the bottom of the bore evenly? The traditional route is to use a boring/facing head. These are specialized boring heads which have an automatic feed on the diameter adjustment of the tool. What that means is that you can lock your milling machine's quill at the bottom of the bore and engage your boring head. When the mill's spindle is turned on, the boring head will cut cross (face) the bottom of the bore. You can bore the diameter of the hole with the same tool but the facing feature disengaged. The only other way to accomplish the two features is by two different milling operations. One, bore the correct diameter hole. Two, face the bottom with, perhaps, a milling cutter on an extension to reach into the hole. The problem with this method is matching accuracy between the first and second operation at the bottom of the hole.

When looking at boring bars, these two procedures are a little at odds. You want to cut the hole and be left with a 90 corner (if I understand you correctly). If you use a boring bar which has a cutting edge flat to the base, though, when you reach the bottom it will chatter. For example, look at these boring bars:


They are flat on the bottom. When that full edge of the insert engages the bottom of your bore, the whole width is trying to cut. That takes a lot of rigidity. So how to solve this? If you angle the insert as some others do, you lose the 90 corner. When you face the bottom with an end mill, you are likely to upset your bore diameter. One way to approach this issue is to use a HSS boring bar and modify it. For example, look at these boring bars:


Same orientation as the previous. Now take a bench grinder and grind a diagonal off:
Now the base engagement is much left, but you retain the 90 corner. There are other ways to do this, of course. I am sure you will gain a few in this thread. Hopefully I have not just confused the matter worse :o

06-25-2011, 07:24 PM
You can always get the 8 inch bar and cut it to the length you need.
That might be the answer right there...
We don't enlarge the hole that much stock case hole is 90mm, open to 96mm
and some to 97.3mm...Heads very simuliar.They make aftermarket big bore piston and cylinder kits for the bugs.They fit with about .010 clearance in the holes.The seal is at the flat ends on the cylinder to the case or head.Metal to metal head and on case side a bead of silicone so no oil leaks.
So i'm really thinking shorten the 8 inch bar unless i like some more input.
Thanks so far ya got my brain thinking better...:eek:
or this ?

06-25-2011, 07:52 PM
With the capacity to accept a 3/4" bar, you've got the option of going to a 1" or larger steel-bodied insert boring bar. You'd cut it to the length you need (as short as practical), then chuck it in a lathe and turn to a shoulder on the shank to 3/4".

The larger bar would allow you to use a fairly large I.C. triangular insert, should you need that 90 flat bottom and don't have a facing action on the boring head. Insert boring bars are available in 1" that have 0 lead with a TNMG331 insert, affording a width of face of over 5/8".

S16T-MTFNR (or L) 3 would be the ANSI designation for the bar.

Careful planning of the modification to the bar would help reduce the chances of chatter. Turn to the sharp, 90 (or slightly less) shoulder, then mill an accurately placed "Weldon" flat for the the set screw to draw the boring bar up tight with the bar's shoulder against the bottom of the boring head's slide. Use a high-positive insert, and you'd be amazed at just how well it works.

I have done this in other applications at one on my jobs (vents on extruder barrels), and it works fabulously. You do need good carbide to turn the insert boring bar, as it can be case-hardened quite deep, up to about 48Rc.

06-26-2011, 05:29 AM
I have had a lot of success making my own boring bars. Just braze a chunk of HSS to the bottom of a piece of CRS round stock and grind the cutting edge flat and 90 degrees to the shank using a solid square as a gage. I've successfully used tools made this way to cut 304 stainless. If possible, as you grind your tool to form stop from time to time and take some practice cuts on a piece of scrap material till it is cutting the way you want it to before going to the actual part.