Boring ‘slightly’ larger holes

[Paul McDonoughParticipant @paulmcdonough43628]

I have got away with using flat bottomed mill tools so far when making largish holes, but I want to set some 22mm diameter ball races into side cheeks of a sub chassis and 22mm is a bit much for my little mill.

So I I’m wondering what is an Economical way to make bigger holes.

I have heard of adjustable boring tool heads but i am not sure if this is the way to go?

cheers

[Tony Pratt 1Participant @tonypratt1]

Yes a boring head is the way to go and I would suggest some practice holes before the real thing. You will also need to buy boring tools to fit the boring head, have a look at Arc Euro trade, Chronos, RDG or online sellers. Come back with further questions as needed.

Tony

[Peter Cook 6Participant @petercook6]

I would agree that a boring head is the simplest way to do it. Arc do a 30mm one that I use on my SX1 mill.

If however you have access to a rotary table, and enough throat on the mill to allow you to rotate the sub chassis on it, then you could use a small milling cutter and mill the inside diameter.

[JasonBModerator @jasonb]

Boring head also works for me.

[SillyOldDufferModerator @sillyoldduffer]

Another vote for a Boring Head, which is a very versatile tool.  Apart from accurately making holes of any size or depth with reach of the cutter, they can hold work in a lathe to cut tapers.

This example comes with a selection of boring bars.  Mine didn’t, and I just use the same bars bought for my lathe.

The boring bars plug into any of the red-ringed holes.  This allows the machinist to select either horizontal or vertical reach to suit the job.

Boring is a slow process but the holes are more accurate than other types.  Finish with several light cuts because boring bars are a bit bendy.

Dave

[Nigel Graham 2Participant @nigelgraham2]

Alternatively can you use a lathe by:

a) Mounting the side-plates, preferably sandwiched together, on the faceplate, or

b) If your lathe is so equipped, mounting the assembly work on the boring-table / slotted cross-slide and machining the holes between-centres,

?

[Paul McDonoughParticipant @paulmcdonough43628]

As ever, than you for your answers, I hadn’t thought of a rotary table but I’d have to buy that too.

I am concerned about space vertically but I can check that when looking at heads and tooling.

I have a related question, how do you know what cutting radius it’s set at?

[Paul McDonoughParticipant @paulmcdonough43628]

Thank you pater, this is of particular interest to me, I have the sx2

[Paul McDonoughParticipant @paulmcdonough43628]

I did wonder about mounting the work vertically on the carriage, but the face plate would be good, I’m just not sure if I have to room to swing the parts.

not sure where the face plate is :0)

im sure I have one somewhere, probably wrapped up in a bag in oil.

[Paul McDonough]

On Paul McDonough Said:

I have a related question, how do you know what cutting radius it’s set at?

In the boring head picture I posted above can be seen a graduated wheel.  It’s turned with an Allen key.  The procedure is to drill a hole of known size, and set the cutter to just touch it.   Then calculate how many graduated turns are needed to reach the wanted diameter, and open up the hole with a series of shallowish cuts.  It’s usual to stop short, measure the hole so far accurately, and do the sums again.   Slow and accurate, not a roughing tool.

It pays to start big holes by roughing them out by chain-drilling, tank-cutting, sawing or trepanning.  Boring heads do a good job converting rough holes into precision centred well-finished and accurate ones.

Dave

[Nigel Graham 2Participant @nigelgraham2]

Paul –

Cutting radius.

It’s worth marking out the material first as a guide.

You see on Dave’s photograph above, the small dial with a central hole – that hole is a hexagon socket for a standard Allen key.

This is the feed dial, in either inch or metric increments, for moving the cutter inwards or outwards. It does not tell you the radius of the hole, only the change in radius you set; analogously to the cross-slide dial on a lathe.

There should also be a locking-screw on the side, probably on the opposite side in the illustration, to hold the slide rigid for each cut.

Take an initial cut to bring the starting drilled or hole-sawn hole to an accurate circular shape and smooth finish, then measure its bore. Then you calculate the radius difference, and use that in conjunction with the dial as on any machine feed-screw.

Bear in mind measuring an internal diameter accurately is not as easy as an external one, with ordinary calipers, and the finishing spring-cuts Dave advises may take the diameter beyond what you think you have set. So you need creep up on the finished diameter very carefully.

For the axial feed, use the milling-machine’s vertical feed-screw, not the quill, for better results.

…

I mentioned “inwards or outwards”. That is because you can, by turning the tool itself round in the holder, also use boring-heads for cutting external diameters such as locating-bosses.

 

 

[HopperParticipant @hopper]

Boring head will generally do a better job  for a precision bearing hole than a rotary table and end mill cutter. So will boring it in the lathe on the faceplate.

Sometimes those carbide cutters supplied with the boring head need a bit of sharpening up before use.

[Paul McDonoughParticipant @paulmcdonough43628]

Thank you guys, this makes sense. I think I’ll give one a go. Hopefully like boring on the lathe it is possible to bore blind holes too.

[JasonBModerator @jasonb]

As Nigel says really for fitting bearings you want to measure the hole the boring head has cut rather than a drilled hole and then use the dial to increase to the desired size measuring the hole to check or in the case of my photo use the bearing as a gauge. Much like boring a hole in the lathe you cut, take a measurement and then put on remaining cuts.

If you want to cut a concave surface where you can’t measure as it is not a complete circle then the radius can be set by offsetting the spindle from a flat surface (usually the edge of the work) by the radii you want. Then turn the haed back and forth as you wind on the cut with the dial until the tip of the cutter just kisses the surface.

One I did on Saturday

Two arcs so it fits the cylinder and flange profiles

Blind is not easy, a stepped hole like the two radii I show above is possible with care and the right shaped cutter but you need good control of the downfeed. For through holes you can just use the quill like you were drilling a hole but to stop at a set depth you would need to use the fine feed on teh SX2. Watch the speed as boring heads soon get out of balance so that may limit your cutting speed and on the SX2 1,0mm on radius would be the around the max cutting depth per pass for roughing 0.25mm or less finish pass

[Paul McDonoughParticipant @paulmcdonough43628]

Thanks, I can see that I’ll need to practice.

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