Creating half a hole

I have a simple project to make two spacers for the attic ladder hand rail, the original plastic ones have become brittle and disintegrated. This requires a 25mm dia half hole in the end of a 25mm ali bar. I can work out two ways to do this, firstly mount it on the rotary table and mill the recess, this has the ready advantage that I have all the tooling, or secondly use a boring head, which I don't currently have but am not averse to acquiring. The question is what is considered the better approach to this task, cost not being a decider, and if a boring head is bought what would be a recommendation?

Regards

Martin

What is your definition of half a hole?

I'm trying to imagine the connection between a boring head and a rotary table, I suppose the rotary table would allow you to create a 'D' shaped (half a circle) blind hole.

Ian P

As Ian has eluded to you don't need a boring head to do the job.
You can use a 2 flute slot drill to mill the straight part of the D all the way though the material.

Then with the tool set at the correct distance from spindle centre cut the remaining shape to full depth by rotating the table back and forth.

Use good clamps and easy cut depths, if possible use an airflow to keep the slots clear of chips.                            Use 12mm ply/mdf or other material below the part so the table won't get damaged.

Emgee.

Edited By Emgee on 23/11/2018 11:01:17

I was reading it as a hemispherical recess in the end of a bar, such that it could butt up against a tube of the same diameter.
If the bar is short enough to fit on a faceplate, centre a length of bar and bore a hole in the middle. Depending on diameters, either cut bar in half, or it will already be in 2 pieces by virtue of the hole being of larger diameter than the bar.

If bar too long to go on faceplate, put a cutting tool in the 4 jaw chuck and clamp the bar to the cross slide.

Use ing the offset of the 4 jaw to change the diameter of the "hole" in the end of the bar.

Bill

If you are doing it in the lathe it might be better to start with a bar a bit larger diameter than 25mm. (Say 35mm. ) You could then hold it in a 4 jaw chuck and bore a 25mm hole right through. (This assumes it is short enough to fit in the 4 jaw.) You could then saw it in two and turn it down to 25mm diameter.

Les.

Grip 25mm bar in the four jaw,or on faceplate, offset by 12.5mm, in the lathe and bore the half a hole with a normal boring bar set 12.5mm over from dead centre (taken in incremental cuts of course.

Bit like this but different

.

Edited By Hopper on 23/11/2018 12:08:19

Hi Martin I assume that these are a round bar with a scallop on the end and a hole through the length for a screw so that the round scallop fits the round handrail to a flat surface. in which case I would do this on my mill rough out a piece of bar whilst clamped in a vee block with a milling cutter as large as I have, about 20mm, then I would bore to size with my boring head to size. repeat on other end to make other one then hacksaw or part off face to length in lathe and drill the hole for the screw. Although you don't have a boring head it is a great excuse to buy one with permission from accountant or purse holder.

David

Edited By David George 1 on 23/11/2018 12:42:09

I see the light now!

I must admit that I looked on 'half a hole' as being 'd' shaped. Must be me but I thought that it might be blind, maybe to sit on a moulded male feature in the ladder construction.

Ian P

Seems complicated for a circular arc at the und of a round bar.

Fly cut, or 25mm end mill. Job done? Or do I have the project over-simplified?

Not at all.

Fit for purpose, come to mind, and for a handrail support the fit of the curved recess against the wall of a bit of tube does not have to be perfect, it could even be hacksawn and filed. We readily accept using a Vee block to hold round work and that only contacts the object at two points.

Ian P

Boring head is how I usually do it, could also plunge cut if you gave a 25mm milling cutter and I would have thought the hole saw fans would have chipped in by now, all ways to do a cope cut.

Here's another suggestion. Use a holesaw bore a hole through a short section of bar, having run a pilot hole through ahead to support the plain part of the guide drill in the holesaw carrier.

Then cut the hole across the diameter to make the two spacers

Regards

Brian

That's what I was thinking Brian, except I would use a Rotabroach to cut the 25mm hole.

If you have more than one to do then just but the ends up in the vice with a bit of packing either side and drill straight through with a blacksmiths drill or any of the above.

Gentlemen

Thank you all for the very useful replies. For reasons too long to explain the Chinese individual who assembled my lathe obviously did it on a Frday afternoon and after a major row with his missus the night before, so it's currently hors de combat whilst I am sorting it, so the project has to be done on the mill.

In practice I am starting with material 25 by 25 by 40 long with a 25mm semi-circular recess on the long side, so drilling is probably out, even though this is far from precision engineering. I don't have either a 25mm end mill or a collet to hold it so there's the best part of £30, which is halfway to a boring head. I have never shied away from buying tools for a job and to a quality that I can best afford, especially when there is a host of other things it can do in the future, so that's the likely route. Thankfully I don't need financial approval for capital expenditure. The rotary table would work but the setup is a bit fiddly, and some of the other suggestions whilst perfectly satisfactory are a problem given the stock size, but my thanks nonetheless for every contribution. There are a lot of very nice people out there.

Regards

Martin

Martin, a bit of 1/2" or 12mm bar cross drilled for a HSS tool bit and withe a grub screw up the end will make a simple single point cutter that will do the job for minimal outlay. Toolbit can be ground from an olfd ctr drill or milling cutter

Thanks Jason.