Boring bar with inserts shape choice??

Well, it all depends. Usually you don't need a dead flat bottom to a blind hole. A normal boring tool taken to the same depth on each pass will end up with only a very shallow "dish" on the bottom of the hole - if that's a problem just make the hole slightly deeper to start with. If you're boring a hole 10mm diameter you'd be b*****y lucky to find a tool capable of facing the bottom. You could always run a 10mm end mill or slot drill down the hole to finish off the bottom. Or maybe use a slot drill to start with as it is by definition capable of cutting to full depth.

I have come across a guy suggesting regrinding a HSS drill end flat with some caveat on what is ground I forget now to achieve a flat bottom. How important here it is is i would imagine not that critical. I have designed ready to go when i have some spare time. As always many ways to accomplish including slot drill, 5 degree cutter (almost flat), End Mill (almost flat) and of course buying in a special tool that would achieve totally flat.

Thanks to all posters

Chris

Chris, the whole reason for you boring the hole is so that it is a good fit on your motor shaft, you can't do that with a reground 10mm drill or a 10mm D bit.

No need for your blind hole to need end facing, you can stop the boring bar just short of where the 9mmdrilled hole goes to which will avoid the beginners luck of running the tool into the end of the hole.

Thanks Jason,

Yes I get that, I was looking into how to face for academic purposes for my notes. I also found out that using inserts / insert holders should be done with some understanding such as triangular verses other shapes lend themselves to certain types of hole machining. For most mild steel and brass I hope I can make my own HSS boring cutters.

What has not been covered is exactly what does happen if the boring bar touches the hole bottom. Does it naff up the tool or bottom or both, or just make the hole longer?

Chris

Hi, I am in severe danger of going off topic but one way of making an adapter is to make an adapter with a 3/8 24 UNF thread to screw into a chuck. My problem is I see the dies for this thread in both R.H and L.H so can any one tell me which I need. Note it is the rod which screws into the thread on the chuck I will be making?

Chris

Frankly I would have thought it obvious if you know which way your motor rotates. But the chances of cutting a true thread with a die are minimal. I wouldn't advise it, you just risk ruining the shaft.

What has not been covered is exactly what does happen if the boring bar touches the hole bottom. Does it naff up the tool or bottom or both, or just make the hole longer?

Depends on a few things, shape of the insert, design of the boring bar nose, material being bored and force with which the tool hits the hole bottom.
One thing for sure is you will know when the bottom of the hole is hit, usually a bit of tool vibration accompanied by quite a bit of noise but not normally any damage with easy to cut materials, if an exotic steel then expect some insert damage.

Always best to set up a bed stop to prevent any of the above events.

Emgee

C’mon, does it really matter if the hole is longer than the bored section? I don’t think so. I think the OP is over-complicating a simple alignment problem. When/if we finally see the finished drawing, it will be a simple job complicated by ‘what ifs’.

Chris see my comment in the motor power thread, you will get a much truer running wheel if you omit what sounds like a drill chuck and fit the wheel straight to the adaptor.

John, how is the way my motor rotates an obvious way to tell me whether the thread should be RH or LH?

Firstly a chuck will come with the 3/8 24 UNF thread, so I need to marry up to this

Secondly the rotational direction of a DC motor is easy to alter by reversing the polarity.

Thirdly It is the drill's motor rotational direction in relation to its chucks thread(if it has one) not my motor which dictates the chuck not coming undone

The answer may be obvious to some but this is beginners question. Helpful advice would have been use a RH thread but I did that myself.

Chris

Chris

With respect, and going back to your post asking whether this should be a RH or LH thread I think it was a pointless thing to ask. The direction of the thread is determined solely by what it has to screw into. Since you have or will have the chuck no one on this forum can answer the question.

A Jason said a chuck, collet or whatever is not going to help making the wheel run true and both will extend the distance from the bearings to the working surface so unless interchangeability is essential it would be best to mount the wheel on the shortest simplest adapter you can make.

As regards threaded drill chucks, they are not generally precision devices unless you pay a lot of money, 99% will have female RH threads but to the mount to make them run true the thread has have a spigot of the correct diameter and a dead square face for the chuck to tighten against.

Lastly, your last paragraph you say that the answer would be obvious to 'some', Are you not one of those?

Ian P

Chucks drive drills and 99.99% of those turn clockwise. So a RH thread on the chuck will tighten up with the reaction torque when drilling. That's why it should be obvious.