questions on boring back to front

[EyeEmTrash]

I have to increase the volume on a part that we make. I could get into all of it but I really just have a few questions about boring as I am still gaining experience in the cnc world. Number one, what are the pros and cons of boring out back to front, instead of front to back? When would that be practically applied? Do I need a special boring bar for it? If I don't ( and this might seem like a silly question but I just want to be sure) do I have to change the rotation of the spindle as opposed to when I do it front to back?

 

[camhead420]

You might want to read the guidelines for posting question's. Your title is very vauge.

 

[jreynolds30]

I have not really seen a huge advantage to boring back to front. Generally you have to take much shallower roughing passes. Spindle rotation is the same direction. I do not recommend back to front boring because there is no real advantages and you will end up increasing part time.

What you need to look at is what your material is, are you using the right insert for the material, can you take a deeper depth of cut, and you increase your feeds and speeds?? Also, can you drill your hole larger to make it so there is less material to remove. You have to look at the big picture.

 

[EyeEmTrash]

I have not really seen a huge advantage to boring back to front. Generally you have to take much shallower roughing passes. Spindle rotation is the same direction. I do not recommend back to front boring because there is no real advantages and you will end up increasing part time.

What you need to look at is what your material is, are you using the right insert for the material, can you take a deeper depth of cut, and you increase your feeds and speeds?? Also, can you drill your hole larger to make it so there is less material to remove. You have to look at the big picture.

I am limited on the tools that I have. The boring bar that I plan on using (just about the only one I can use realistically for this new op) is one that I have never used before. It uses what I believe is a V insert (long and thin diamond) and I thought that it was tilted toward the back end of the tool. It isn't. I have always used just regular diamond or triangle inserts for boring. I was confused and thought that it was maybe a special kind. I am not the brightest sometimes.

 

[William Lynn]

I have found that boring back to front can reduce chatter. Cutting front to back, the force is trying to bend the bar, possibly causing it to bounce and createse chatter. Cutting back to front, the force is trying to stretch the bar with less bounce. Something to do with harmonics. There are many variables involved, but sometimes it works.
I had a few parts I made that needed a big chamfer on the back side before through threading. I would bore normally, then for the finish pass, I cut the chamfer on the back side and finish the bore by cutting back to front. It worked better that way.

 

[Booze Daily]

I do it on plastic. It brings the chips out with it so they don’t melt in the bore.

 

[sinha]

Unless the tool is of neutral type, it should not normally be used for machining both ways.
Therefore, for a given tool, there is not really a choice for the direction of machining.

External tools can be inverted for reversing the direction of machining.

 

[angelw]

Unless the tool is of neutral type, it should not normally be used for machining both ways.
Therefore, for a given tool, there is not really a choice for the direction of machining.

External tools can be inverted for reversing the direction of machining.

That's not necessarily correct. As just one example, with a client's recent job where a flange welded to a shaft had sustained quite an amount of distortion, but not enough that the front surface of the flange (facing towards the right) that had to be machined, wouldn't clean up, the edge between the flange OD and the back surface of the flange was difficult to debur due to the run out of the rear face. Machining from small diameter of the flange towards the larger diameter, then the OD towards the chuck, resulted in a very severe bur. Machining the Flange OD from the chuck towards the right solved this problem.

On very stringy material, I've used boring bars with VNMG or DNMG inserts, set with a forward pointing approach angle, to machine from the bottom of the bore in a L to R cutting direction, so that the swarf is pulled out of the bore. The only real issue is feeding the tool in to take a reasonable DOC. Accordingly, you have to be either satisfied with a reasonably small DOC, or cut a groove at the bottom of the bore into which to feed the insert to set the DOC. As there is a thinning of the chip feeding in that direction, the feed rate can normally be increased.

Regards,

Bill

 

[William Lynn]

Unless the tool is of neutral type, it should not normally be used for machining both ways.
Therefore, for a given tool, there is not really a choice for the direction of machining.

External tools can be inverted for reversing the direction of machining.

The boring bar in my example used a DNMG insert at a 90. Thinking is was a DDPN bar.

 

[gregormarwick]

I do my finish pass outwards fairly often when I am boring something that doesn't chip well with a small DOC and I need a very good surface finish. It prevents swarf scoring effectively.

 

[wesg]

I've done it on an engine lathe, feeding radially to shy of chatter and then away from the bottom .1" or so ... and repeat until I have a decent DOC before making a full pass out. Saves a massive amount of time stopping the spindle to fish the 'wool' out of the bore, before you can even get to full depth.

Shouldn't be too hard to program something like this by hand. I switch Abs/Inc on the mill quite often for sub's rather than using multiple coord's.

 

[michiganbuck]

If one had a through-hole bore it seems like a square insert with a scalped side edge facing the inside of the bore could cut going both directions. Yes, the following would drag a little but would be turning correct. it would go half way past each end of the part.
The savings would be the time it takes to return to the starting position. so not much time going in rapid..