Drill or mill?

[Paulc]

Have a .75 aluminum round, .5 inch long and it needs a .5 inch hole thru.
Better to drill or mill?

[crueby]

For a really round hole, I would chuck it in the lathe, drill a starter hole through it, then take it out to size with a boring bar, all on the lathe. Nice round centered hole.

[Jasonb]

Same here

[Craig DeShong]

Use the lathe definitely.  If you have a1/2 inch ream, drill undersize, then ream.

[Paulc]

After fooling with a Chinese boring bar set for half an hour and getting crappy results, I finished it with a 1/2 in drill in the lathe tail stock and the results were very good.
 Did a second one by progressively drilling a larger hole after starting with a center drill and that went smoothly as well.

[steamer]

There are lots of articles on making a decent boring bar for HSS tools and carbide as well.     Learn to do it, and it's a tool you'll be glad you have

Crueby is quite right.....for the best hole, drill undersize, then bore to .005" under  (0.050 mm under) and then run a reamer through slow and steady.   Dead on size, and dead on position, but the the order is critical

A drill makes a hole...it's neither round  or straight....and it's got an approximate size....though often bigger than the nominal drill size.

The boring bar makes the hole round, and straight, and concentric to the lathe spindle....

Now that the hole is round, straight and concentric, your reamer will follow the good hole and give you a hole that is also to size.

If you're careful, you can bring the hole to size with the boring bar, easy peasy.

Dave

[crueby]

I have also tried the cheapo boring bar sets, with (badly) welded on carbide tips. Pretty worthless tools, at least as they come, usually the cutting edges are dull, at bad angles, geometry of them is badly done, and the shanks are too flexible. I switched to better solid piece carbide bars and/or ones that take a small-radius insert, and got much better results. The shorter the bar is extended out of the holder the better, and the height/angle makes a difference.

[Paulc]

OMG! More tooling to buy!!
Do those Chinese boring bars work any better in a mill boring head?

[steamer]

They generally have all the wrong angles on the cutting edges....and that makes them rub alot...they need to be reground....Let me see what I have in my article bin....

Dave

[Jasonb]

With the brazed tip boring bars a lot depends on which one from the set you use. If you don't know what you are doing it's easy to pick up a short stubby one thinking it will be more rigid and find it does not work in a 1/2" hole. Reason being it's probably ground for a 2" dia hole so clearance angles will suit that and not a small 1/2" hole.

I've used ones that cut straight out the pack and also modified ones for particular uses.

Same thing with insert boring bars, both lathe and boring head ones, they all have a minimum hole size and will rub if you ttry and poke them up a hole that is too small.

Very cheap far eastern is a bit of a lottery but reasonably priced far eastern does the job in the right hands.

[Paulc]

The grind on this set of six appears to be the same for all lengths, but the length of the carbide piece seems to increase as the bar itself gets longer.

[Jasonb]

have you got a link or photo of them?

[steamer]

Here are a couple of references for DIY boring bars that take round HSS or Carbide blanks that you then grind.

a 90 degree and a 45 degree set is good as it lets you bore to the bottom of a blind hole

<a href="https://www.youtube.com/watch?v=chiJb7Xp2rk" target="_blank">http://www.youtube.com/watch?v=chiJb7Xp2rk</a>

I'm sure I can find a set of drawings for one, but if you're not looking to make a set of boring bars....here's a double end set for cheap money

https://www.busybeetools.com/products/boring-bar-set-4pc-1-4in-5-16in-3-8in-1-2in.html

My set is below...down to 3/16"

[Paulc]

have you got a link or photo of them?

Will try to get some photos later today.

[Paulc]

Here's the best i could get of the boring bars. The varying lengths raise havoc with the auto focus.

[john mills]

similar sets of brazed on tools with i have seen and used are only partly ground and require finish grinding before use   then they can work very well.most of my tools are brazed on ,i have made my self  mild steel shank and a
 insert based on   then ground as required.

[steamer]

Here's the best i could get of the boring bars. The varying lengths raise havoc with the auto focus.

Yes   and you'll notice that the cutting edge is way above the center of the bar...so if you put the tool in the mill with the bar at center of rotation the cutting edge isn't.  To get it there you end up rotating the bar and you get negative top rake....not a good thing with a boring bar...it makes them chatter.

You can make them work somewhat in the lathe as you can mount them with the cutting edge at center, but you have to watch the flanks or you won't have enough clearance and they'll rub....also not good.

Dave

[Jasonb]

Well looking at the photo I certainly see different angles on the tools, take the middle row, one on the left has very little angle and one on the right quite a bit more as shown in yellow.

Now try those in a hole and see what size it needs to be before the back edge starts to rub and you can see why you had problems is trying to get any of those to machine a 1/2" hole. Green shows minimum size they would suit. Would need to be even larger if you want to cut with more top rake on the tool.

[Chipswitheverything]

Hi Paul, for conveniently boring this sort of smaller sized hole there is a lot to be said for making up a few small boring bars yourself from silver steel, the length and shape of the cutting edge can be produced by turning and filing the s/steel in its unhardened state, and then the tool can be hardened + tempered, and the final edge put on by honing with a slipstone.
 It is easy when filing the cutting edge to be sure that you give it the clearances that will work in the small dia holes.
  The tools work best in conjunction with a simple holder made up to fit the tool post arrangement that you are using.  There is much about all this in the articles and books written by the late Geo. H Thomas, who designed a lot of tooling for the model engineer and wrote the designs up in Model Engineer magazine.  Dave

[Paulc]

Well looking at the photo I certainly see different angles on the tools, take the middle row, one on the left has very little angle and one on the right quite a bit more as shown in yellow.

Now try those in a hole and see what size it needs to be before the back edge starts to rub and you can see why you had problems is trying to get any of those to machine a 1/2" hole. Green shows minimum size they would suit. Would need to be even larger if you want to cut with more top rake on the tool.

If I understand you correctly, the smaller the hole to be bored requires the angle on the tip to be more acute? There appears to be quite a variation in the angle between the smallest and largest bar in the set.
Guess I'd need some schooling on what the configuration should be for various minimum diameters.