Author Topic: Drill or mill?  (Read 682 times)

Offline john mills

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Re: Drill or mill?
« Reply #15 on: November 04, 2019, 06:03:36 AM »
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.

Offline steamer

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Re: Drill or mill?
« Reply #16 on: November 04, 2019, 02:55:30 PM »
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
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Online Jasonb

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Re: Drill or mill?
« Reply #17 on: November 05, 2019, 07:36:52 AM »
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.



Offline Chipswitheverything

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Re: Drill or mill?
« Reply #18 on: November 05, 2019, 01:52:53 PM »
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

Offline Paulc

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Re: Drill or mill?
« Reply #19 on: November 05, 2019, 05:15:36 PM »
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.