Micro boring bar

[Alberto-sp]

Hello. I´m working with very small parts and I need a small boring bar.

I saw these options



I think the best one to work with holes and bottoming, I mean, to remove material in a hole in the red zone of this picture



the most suitable one culd be the MUR, MTR or MPR, but I´m not sure. Wich one do you chose?

Thank you

Best regards

 

[ivel03]

I think any of those will work. Depending on your lathe size it might take less power to run MPR if it has a sharper point but it will likely be slower and not leave as nice a finish. If the "bottom" of the hole needs to be at 90* then the compound will need to be rotated such that the end of the cutter is parallel to the face of the part. If you have an broken old end or drill bit and a bench grinder you should be able to make one - it might be worth a try while one is on order.

 

[GL]

In many cases, HHS ground to the shape you need is preferred to the romance of a brazed carbide tool. In many cases, depending on the material you are cutting, HHS is preferred for surface finish especially in small parts where you need high speed to make carbide work. Watch your back angles and clearance angles. Lots of youtube videos on that subject from oxtool, blondihacks , Mr Pete, abomb79, etc - the usual suspects. Grinding your own tools isn’t that complicated, but maybe a little intimidating at first. Gives lots of confidence in the long run though. Amazing what you can do with a little patience and a grinder, plus you can screw it up and recover easily with a little practice. If you look in an old machinist’s tool box, there’s always a bunch of weird looking tool bits ground for some special purpose. We are trying to make something that doesn’t exist, with the tools available, or we can create. Make the tools and your creativity work for you. That’s the fun in the process. And you aren’t limited by what you can buy. Have fun, good luck, be safe.

 

[Provincial]

If the hole is big enough I use a forged HSS bit from a boring head set. I don't know if anyone supplies these any more, since carbide has taken over. The HSS bits are more compact than the carbide units, so you can get in a smaller hole.

Another way is to get some tool steel, heat it and make the offset end, then harden it. After it cools ,grind it to the desired shape.

 

[Alberto-sp]

Thank you' I'll try it.

By the way, about carbide, I know one of the advantages is that it can work at very high speeds, but it works badly at low speeds or simply at low speeds you don't take advantage of it? I mean, is there any problem with working with carbide at low speeds?

Thank you

 

[Illinoyance]

MPR will allow you to face the bottom of the hole after boring. A bar with a 90* end will probably cause chatter when it contacts the end of the bore.

 

[Alberto-sp]

Thank you!

 

[Illinoyance]

Alberto, there is another option. You can grind a boring bar from a square tool bit if you have a grinder and the patience.

 

[ChazzC]

If the hole is big enough I use a forged HSS bit from a boring head set. I don't know if anyone supplies these any more, since carbide has taken over. The HSS bits are more compact than the carbide units, so you can get in a smaller hole.

Little Machine Shop has a set of 3/8” shank M35 HSS boring bars, but since they’re not as common as brazed Carbide, they cost 3x as much. And, you you noted, diameter/depth may not work for @Alberto-sp ’s application.

 

[G-ManBart]

Thank you' I'll try it.

By the way, about carbide, I know one of the advantages is that it can work at very high speeds, but it works badly at low speeds or simply at low speeds you don't take advantage of it? I mean, is there any problem with working with carbide at low speeds?

Thank you

Carbide works fine at lower speeds. It may not give the absolute best surface finish, and it may not be the most economical choice, but for most things it's fine. It's really just a matter of trying different speeds and feeds with a particular type/size of stock to see what happens. Carbide allows for high speeds, high feeds, etc but doesn't necessarily require them. Yes, it's possible to go too slow, too shallow, or too low a feed rate and get bad results, but that's true of anything.

A couple of months ago I bought a SB Heavy 10 as a fun project. I put a QCTP on it with an SCLR tool holder which uses CCMT inserts, set the tool height on center and this was literally the first cut I made with that setup....guessed at speeds and feeds going off what I use on my other lathes. This was on the 585rpm pulley configuration, so not fast at all. It actually looked better in person and was darned near a mirror. I'm sure lots of folks can do better, but I was happy with the result...especially because it was mystery steel.