Drilling large holes

[Mike PooleParticipant @mikepoole82104]

[Mike PooleParticipant @mikepoole82104]

Most hobby mills run out of headroom if it is desired to mount a large drill. I have been toying with the idea of buying or making an adaptor to use Rotabroach style cutters, being a treppaning type operation less power is required and the cutters are available in short lengths and large diameters. Has anyone tried this? Did it work? What does the panel think?

Mike

[David ColwillParticipant @davidcolwill19261]

This is on my to do list. I have seen several people on youtube use them to great effect. I am just waiting to happen across the cutters at the right price.

Regards.

David.

[David ColwillParticipant @davidcolwill19261]

I should also say that I would want to use them on the lathe as well.

David.

[Peter SpinkParticipant @peterspink21088]

Bought one to cut some 28mm holes in 4mm brass. Only slight problem is the size of the shank which is too big for any of my collets. Used a small three jaw chuck instead with no issues and cut lovely clean holes.

Peter

[BikepeteParticipant @bikepete]

Use them often, held in an ER32 collet. Bigger ones are usually available fairly cheap at a local autojumble.

[clogsParticipant @clogs]

Hi all,

I use them all the time in my Colch/Student 6" and both my mill's……I also use a mag drill machine quite often……..

I use the R8/er32 collet holder in the mill and the correct mag drill bit holder in the tail stock, MT3 (I think)….

Works a treat, just use a slow speed (RPM) and plenty of cutting fluid…….

Clogs……..

[Dan CarterParticipant @dancarter89683]

I started using them on my X2 whose motor was too puny for big holes – they work really well. I made a holder including a sprung pilot pin for hole location. My new Mill is r8 and has dro, so can use 3/4 inch collet directly and hole location mostly not an issue.

The smaller ones are pretty cheap on Amazon, and msc had them on special offer last month so worth keeping an eye on.

[Mike PooleParticipant @mikepoole82104]

Thanks chaps, that seems like a positive endorsement, I will sort out an R8 adaptor for the mill and a morse 2 for the lathe. I think a rotation stop will be prudent with MT2 on the lathe, I imagine a larger cutter will need quite a bit of torque and MT2 is not used for drills over 22mm. Will give it a go!

Mike

[Tim StevensParticipant @timstevens64731]

I have had success with holes saws from the usual E source. Not the 'traditional' wavy saw tooth versions from builder's merchants. There are two types – one with a ring of ground teeth, and the others with a few carbide tipped teeth. For aluminium or brass sheet up to about 4mm, round holes and smooth. Also handy for generating spheres.

Cheers, Tim

[SpurryParticipant @spurry]

Only problem I have found is that you have to be very diligent with clearing the chips away, unless on thin material. They work well.

Pete

[Mark CParticipant @markc]

As Tim, I have used conventional "builders" hole saws (the better quality ones) and have hacked my way through 12mm steel plate at 100mm diameter! You do need to use cutting fluid and keep the swarf cleared or it blocks the gullets and they stop cutting

Mark

[not done it yetParticipant @notdoneityet]

I bought a 'practool' years ago. It has done me sterling service over the years. Up to 40mm is no problem, apart from setting a specific size accurately.

http://www.practool.com/super-drill.html

[Robin KingParticipant @robinking15611]

Peter Rawlinson's article in MEW Sept/Oct 1996 gave a useful intro to their use. I've since picked up a few from a local steelwork fabricator but haven't had a chance to use them yet. They stock a wide range of them in their stores shop so I'm hoping to get a few more.

[Martin 100Participant @martin100]

I first used holesaws in the lathe in the mid 80's to cut 2 inch diameter holes in circa 3/4" steel followed by a boring operation. Mainly using the off the shelf yellow starrett holesaws as they were freely available.

I have some rotabroaches dating from I'd guess the late 1970's from 1/4" up to about 3/4" but they are still unused sat in a drawer in the toolchest.

[RobboParticipant @robbo]

Have used Rotabroach cutters for years, having made an arbour for them, including the pilot. After having bought one on ebay for a pittance, out of curiosity. Soon bought several more. Excellent hole cutters.

Carry on Mike.

[Peter SpinkParticipant @peterspink21088]

Posted by Robbo on 16/01/2017 23:17:27:

Have used Rotabroach cutters for years, having made an arbour for them, including the pilot. After having bought one on ebay for a pittance, out of curiosity. Soon bought several more. Excellent hole cutters.

Carry on Mike.

Having only ever bought one so far, is the shank size standard over a range of sizes?

i.e. if I make an arbour for the one I've got, will it be useful in future?

Peter

[John ReeseParticipant @johnreese12848]

Posted by Peter Spink on 16/01/2017 23:24:32:

Posted by Robbo on 16/01/2017 23:17:27:

Have used Rotabroach cutters for years, having made an arbour for them, including the pilot. After having bought one on ebay for a pittance, out of curiosity. Soon bought several more. Excellent hole cutters.

Carry on Mike.

Having only ever bought one so far, is the shank size standard over a range of sizes?

i.e. if I make an arbour for the one I've got, will it be useful in future?

Peter

All sizes have a 3/4" shank.

[BWParticipant @bw]

Posted by Tim Stevens on 16/01/2017 18:30:44:

Also handy for generating spheres.

Cheers, Tim

Am guessing that its similar to the sphere generation by boring bar ?

ttps://www.youtube.com/watch?v=BJtxfI_LKio

Bill

[Tim StevensParticipant @timstevens64731]

I cannot say what Bill Wood is guessing, but I guess that he is right. The advantages are that you get several teeth rather than one, and that carbide is an off-the-shelf option for difficult materials. The disadvantage of a fixed cutting radius is not so serious in practice, and is hardly relevant when you look at the range of diameters available at very modest cost.

Here is a random example with tool diameters from 16mm to 50mm and prices from about £4 to under £7:
**LINK**

Cheers, Tim

[SpurryParticipant @spurry]

Just found an old picture I had taken last year. Fits a 20mm R8 collet.

Pete

[Raymond AndersonParticipant @raymondanderson34407]

G& J Hall [ Powerbor ] are excellent cutters. Should work fine in a mill.

[BWParticipant @bw]

Posted by Tim Stevens on 17/01/2017 08:54:19:

I cannot say what Bill Wood is guessing,

Cheers, Tim

Tim,

Am exploring the different ways of cutting the bobbles on the end of my chess pawns.

So am genuinely curious about your method for making balls using this type of cutter.

Is it similar to the boring bar idea in that link or something completely different ?

Bill

[Tim StevensParticipant @timstevens64731]

Yes, indeed it is, Bill. One difficulty with a boring bar as shown in the clip is the need to have cutters which are properly shaped on the inside – which those sold for boring heads generally are not. Also, you need to be aware that the head part of the boring head is threaded and screwed onto the taper part. This makes using such a device backwards fraught with disaster, as the intermittent cut is likely to unscrew it.

Both designs of cutter I describe have sensibly shaped teeth, although in practice they are not all 100% true to the tail on which they are mounted. So, one tooth can do most of the work, which is what you have with the boring-head method anyway. A further advantage is that when the 'main' tooth becomes worn or chipped etc, you can grind it away and still have the others to do the same job.

To generate a sphere the cutter size inside needs to be smaller than the diameter of the sphere, and should trace a line over the whole area required. For a knob as are used on many lather controls (Myford etc) the cutter needs to be tilted so that the inner edge crosses the axis of the rotation of the work. A few sketches will enable you to work out what will work for the size of sphere and the radius of the finished bar, leaving an internal corner to be blended with a radius on a lathe tool.

Come back to me with a PM if this does not make sense, and I will send you a photo or two.

Regards, Tim

[ianjParticipant @ians]

Just a heads up. Cromwell tools have 14mm & 18mm short (25mm) rota broach cutters for sale at 78p & 89p respectively, inclusive of vat. Free postage on orders of £20. Their silver steel is a good price as well.

Ian

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