Line boring bar diameter advice

[CRS51]

These two are good:

Learn the boring bar ISO code system!

Learn the boring bar ISO code system!

www.cutwel.co.uk

MMC HARDMETAL U.K. LTD

www.mitsubishicarbide.com

For your bar: (S) steel (12) 12mm dia. (M) 150mm long (S) screw mounted insert (C) insert shape (L) lead angle 95 degree (C) relief angle 7 degree (L) left hand (06) insert size 06.

For the insert: (C) insert shape 80 degree rhombus (C) clearance 7 degrees (compare with relief in the bar code) (M) tolerance. M is standard; only other common one is G (for ground) (T) fixing method hole (compare with screw mounted for bar) (06) insert size, same as bar code (02) insert thickness (02) corner radius. The HMCTP125 is likely specific to the insert manufacturer.

One thing to note is that the corner radius has a big bearing on the fragility of the insert. A larger radius (06 inserts can be had in 00, 02, 04 & 08) might help with the type of cut you are doing - maybe the 08 radius for the first pass of the welded bore and then change to an 04 or 02 for finishing. Using an 02 from the start may be one of the reasons for the broken tips you mention.

I could only find one reference to your insert, from protool, and they do not provide a translation of the manufacturer-specific part. If you go for a brand name insert, there will be a data sheet available with this info. on it. One thing to note is that carbide is available in different grades - some are tougher then others, some more wear-resistant than others. For the initial pass of the welded bore, you need an insert with the maximum toughness until you have removed enough material to obtain a uniform bore.

Even if you go for an HSS tool as suggested above, the grind on the roughing tool will be quite different to that of the finishing tool.

Thankyou @Agroshield I will have a good think about what you have written.
It’s all a learning curve at present.
I should have stated that the bores have not been welded up in any way as we thought this may complicate things further.
The plan is to take out just enough to get a round hole in each of the bits that need doing then we can have a bush made up to fit.
The 2 sizes chalked on are what we stated with and the size we ended up with to get a true hole.
Hope that all makes sense lolol
Chris

 

[MickeyW]

You've done a fantastic job there Chris, great surface finish and on a much bigger scale than my own efforts.

 

[CRS51]

Another 2 holes done yesterday. I have a question though, the carbide inserts have a guide of 120 - 360 m/min, I am presuming that this is the speed of the workpiece or insert at the point of work.
How would I convert the above to rpm’s so we can see if the mag drill speed we are using is correct for the insert ?
The round line in one of the pics is where the side of the bucket has met the next part before being welded up.
Cheers Chris

 

[Agroshield]

...the carbide inserts have a guide of 120 - 360 m/min...

For what you are doing, just ignore those numbers. What sounds and looks right and what gives acceptable finish and insert life is more important than any number.

You are correct that the numbers given are surface speed in metres per minute. Just as your car speedo displays in miles per hour - the speed at which the car travels over the road surface, so the insert surface speed is how fast it travels over what it is cutting.

So, if the circumference of what it is cutting is 1m (which would make the diameter about 318mm) and the tool is rotating at 1 rev. per minute, your surface speed would be 1m/min. If you rotate the tool at 1000 rpm for the same diameter, its surface speed would be 1000 m/min (or 60km/h). If you rotate the tool at 1000 rpm but the diameter is 100mm, the circumference is 0.314m so your surface speed would be 314 m/min.

As an exercise, see what the maximum speed of the rotabroach is and work out what diameter you would have to cut at that speed to achieve 120m/min.

 

[Rrobson]

It’s surface speed of the work at the point of the tool or the surface speed of the tip of the tool.
The equations you need are

Metric

V = 60 x 1000 x surface speed m per min
—————————
3.142 x dia of work in mm

Imperial

V = 12 x surface speed feet per min
————————
3.142 x dia of work in inches

 

[Pete.]

Here's a chart from 30-150mm for your range of surface speeds.

 

[CRS51]

For what you are doing, just ignore those numbers. What sounds and looks right and what gives acceptable finish and insert life is more important than any number.

You are correct that the numbers given are surface speed in metres per minute. Just as your car speedo displays in miles per hour - the speed at which the car travels over the road surface, so the insert surface speed is how fast it travels over what it is cutting.

So, if the circumference of what it is cutting is 1m (which would make the diameter about 318mm) and the tool is rotating at 1 rev. per minute, your surface speed would be 1m/min. If you rotate the tool at 1000 rpm for the same diameter, its surface speed would be 1000 m/min (or 60km/h). If you rotate the tool at 1000 rpm but the diameter is 100mm, the circumference is 0.314m so your surface speed would be 314 m/min.

As an exercise, see what the maximum speed of the rotabroach is and work out what diameter you would have to cut at that speed to achieve 120m/min.

It’s surface speed of the work at the point of the tool or the surface speed of the tip of the tool.
The equations you need are

Metric

V = 60 x 1000 x surface speed m per min
—————————
3.142 x dia of work in mm

Imperial

V = 12 x surface speed feet per min
————————
3.142 x dia of work in inches

Here's a chart from 30-150mm for your range of surface speeds.

View attachment 341376

Thanks all, plenty to try and get my head around and work out, will report back

 

[CRS51]

Finally finished the bucket clam line boring, we are on with getting pins now.
Pins will be turned down to suit bore diameter and that will then give me internal measurements for the bushes needed for the rear part of bucket. Hope this makes sense.
Things I have learnt,
it is a slow process,
everything must be braced as rigidly as possible,
speed and feed play a big part in insert life.
Cheers Chris.

 

[8ob]

@CRS51 , That is some achievement, seriously impressed with this from start to finish

Bob

 

[Brad93]

Looks like you've got some chatter but to be expected with the setup.

It's all a learning curve aye.

 

[CRS51]

@CRS51 , That is some achievement, seriously impressed with this from start to finish

Bob

Thanks Bob, we have some more to do in the future

 

[CRS51]

Looks like you've got some chatter but to be expected with the setup.

It's all a learning curve aye.

Cheers Brad, yes a lot to learn, the worst bits were the cast steel lugs that are welded to the top of the clam sides, seemed to have very hard / tough spots in them, maybe someone had been welding in there in the past.
Chris