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Slot cutting

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Clock polisher03/01/2022 19:18:09
21 forum posts
32 photos

Good evening,

I am a complete novice with regards to milling operations. I have a Unimat SL lathe that can be converted into a milling machine.

I wish to machine slots in two pieces of aluminium that will fit around and clamp to a 12mm diameter steel bar, so the slots would be not quite semi-circular. The alumimiun is only 20mm thick where this is required.

Will I need a ball end cutting tool? I've seen them for sale at over £40 and as this is a one-off job that's a bit pricey. Is there anything else I could use, or would it be much easier to drill a 12mm hole in an over-size piece and then saw it in half.

Any suggestions greatly appreciated.

kindest regards,

David

Clive Brown 103/01/2022 19:30:43
807 forum posts
39 photos

Drilling and sawing across would be easier, quicker, cheaper and more accurate.

Other than the above there's nothing to choose between the methods!!

JasonB03/01/2022 19:53:03
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22585 forum posts
2638 photos
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If you have two bits you won't even need to saw, just clamp them together with a thin packer between and drill then bore/ream to your 12mm,

Alternative will be to clamp the two bits together, bore and then machine a little off one or both mating surfaces so that they can then close up onto the 12mm rod when clamped.

Clock polisher04/01/2022 19:00:30
21 forum posts
32 photos

Good evening,

Many thanks for your replies.

I'll go down the route of drilling two pieces whilst clamped.

kindest regards,

David

Emgee04/01/2022 19:42:33
2404 forum posts
285 photos

David

If you have a 4j chuck it may be big enough to hold your blank to drill and bore the 12 mm hole,

If you don't have a 4j but you have a faceplate you can fix your blank to that to drill and bore to size.

In both cases you will have to add packing between the f/plate and blank material to allow the drill and boring tool to pass through.

Unless you have the slow speed attachment the minimum speed will be too high for even a 12mm machine reamer, unless you have changed the original motor.
You could of course use a hand reamer with the part held in a vice, if so bore the hole to something like 11.80mm.

Emgee

JasonB04/01/2022 19:58:59
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22585 forum posts
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Though one can always use the machine to guide a hand reamer while rotating it or the work by hand, did that plenty of times on my U3

3 Jaw lathe chuck makes for a good large capacity drill chuck too as you work up in small steps to the largest size you need.

Emgee04/01/2022 21:23:12
2404 forum posts
285 photos
Posted by JasonB on 04/01/2022 19:58:59:

Though one can always use the machine to guide a hand reamer while rotating it or the work by hand, did that plenty of times on my U3

3 Jaw lathe chuck makes for a good large capacity drill chuck too as you work up in small steps to the largest size you need.

Not sure you can Jason, not with a 12mm taper reamer as the hole in the spindle is only 6.35mm so the reamer would bottom out before the 12mm parallel part had had reached the back of the part, you would need to remove the part and hold in the vice to complete the reaming, so it is an alternative method to ensure a reamed hole square with the surface.
If bored to 12mm for 1mm depth to act as a guide a machine reamer could be used as you suggest.

I will get my SL out and check the dimensions for the stated material thickness.

Emgee

not done it yet05/01/2022 08:12:34
6736 forum posts
20 photos

Not sure what the problem might be. Could you not drill the holes in the appropriate positions and turn off the metal until only half the hole is left? A plain milling cutter (or slot drill) could be used to make the slot slightly less than circular. Just some improvisation required to suit the purpose, I think.

Clock polisher06/01/2022 19:19:00
21 forum posts
32 photos

Good evening,

I will use the drilling technique between two pieces of bar as the accuracy of a reamer is not required.

The aluminium should be here next week.

I have been making some clock parts that are over 100mm long recently. The Unimat SL has a long travel leadscrew with a thread pitch of 1.0mm. This makes these operations a little tedious.

I've put together the required equipment to fit a stepper motor to the long travel. This will run in either direction using push buttons and be speed controlled, independent of lathe speed.

Part of this equipment is a third party motor mounting bracket that wasn't all it should have been when it arrived. The section that fits underneath the bed bars of the lathe and holds the motor is fine, the clamping piece that holds this to the bed bars is not. It is this piece I will be remaking.

80mm long by 20x30mm section with two 12mm slots in it to fit snugly over the bars. Two M6 bolt holes to complete.

kindest regards,

David

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