Milling a square channel

[sean logieParticipant @seanlogie69385]

I’m going to be milling two square channels the full width 130mm in a steel plate about 20mm deep and 15mm wide . My question is ,do I use a 15mm roughing endmill and do it in several passes for the depth . Or should I use a smaller end mill for the same procedure . Lastly 2 or a 4 flute .

Sean

[sean logieParticipant @seanlogie69385]

[Martin ConnellyParticipant @martinconnelly55370]

Totally depends on the machine you are going to use.

Martin C

[SillyOldDufferModerator @sillyoldduffer]

With a WM18 (Chinese, 220kg, 1100W motor), I'd use a 15mm 2-flute HSS at about 600rpm and go down about 2mm – 1.5mm per cut. As it's a big job, I'd flood cool it.

Actually, as I don't own a 15mm end-mill, I'd use 14mm to rough out the slots and then finish off by widening it. A more powerful machine could probably do 3mm deep cuts. A smaller machine should be reduced according to how powerful the motor and how rigid it is. Rule of thumb, use biggest end-mill available and cut up to about 20% of the diameter of the end-mill. Above 20% you risk bending or breaking the tool. Small machines may not have the grunt to take 20% cuts plus chatter due to lack of rigidity.

I'll be interested to see what others say.

Dave

[sean logieParticipant @seanlogie69385]

I’ll be using a Centec2 horizontal mill with a mt2 collet.

Sean

[sean logieParticipant @seanlogie69385]

I’ll be using a Centec2 horizontal mill with a mt2 collet.

Sean

[JourneymanParticipant @journeyman]

Out of interest why not use the Centec as a horizontal mill? With a suitable cutter it would probably be a quicker job, big slots are what horizontal mills are good at.

John

[sean logieParticipant @seanlogie69385]

Great minds n that 😉

Sean

[Andy MurrayParticipant @andymurray87642]

A ripper is the best choice and will do it in 3 to 4 depth cuts, if it's a 4 flute I would slow the rpm down a bit. Speed burns HSS out .

Andy

[vintagengineerParticipant @vintagengineer]

Horizontal mill will do it in one pass at a slow feed rate.

[not done it yetParticipant @notdoneityet]

Horizontal mill will do it in one pass at a slow feed rate.

With a half horsepower motor, needing a minimum 3" diameter cutter, with likely a dozen cutting edges, feeding at sufficient rate to avoid rubbing (with no power feed available)? I think that is a bit optimistic.

[sean logieParticipant @seanlogie69385]

Ooft..the old centec2 would struggle doing it in one pass I think 😁

Sean

[SillyOldDufferModerator @sillyoldduffer]

Typical power requirements (in Watts per second) needed to remove a cubic millimetre of metal are about:

• Aluminium 0.4 – 1
• Cast Iron 1.1 – 5.4
• Brass and Bronze 1.4 – 3.2
• Magnesium Alloys 0.3 – 0.6
• Stainless Steel 2 – 5
• Steel 2 – 9

Note the power figures depend on the alloy being cut. In the case of steel, 2 would be right for mild steel, but a lot more oomph is needed to cut one of the hard tough alloys.

Assuming Sean wants to cut a 130 x 20 x 15 slot in mild-steel. That's 39000 cubic millimetres of steel. At 2Ws per cubic millimetre, the electricity bill will be about 79000W seconds. From that you can guesstimate the minimum time would it take a particular motor to cut the slot.

• 3000W would take 26 seconds
• 2000W – 39 seconds
• 1000W – 78 seconds
• 750W – 104 seconds
• 500W – 156 seconds
• 375W – 208 seconds

The time estimates assume that feed-rate and depth of cut don't matter. They do! For mild steel using carbide, the depth of cut should be in the range 0.15 to 7.6mm with cutting rate between 60 and 135 metres per minute. Even on a big machine the maximum depth of cut suggests a minimum of two passes.

It's not the law though, industrial cutting rates are carefully calculated to minimise cost by balancing of power, machine capability, tool life, and production time. Big machines can and do take deeper cuts. Not so clever in a home workshop I think where our machines are likely to be relatively small, not very rigid, or worn. Better to proceed by feel and experience than calculation.

How powerful is the motor on Sean's Centec? That plus the machine's lack of rigidity will determine how many cuts it will take him to do the job.

Dave

 

Edited By SillyOldDuffer on 29/11/2017 11:33:36

[sean logieParticipant @seanlogie69385]

That hurt my head 🤡😁😉

Sean

[HOWARDTParticipant @howardt]

After removing all that metal you may find you have a banana. Have you thought about straightening, maybe having to stress relieve. I refer to the part not yourself. If you have enough material if it bends doing it in a single cut, leave metal on and stress relieve before straightening and then do a finish cut.

[Dave HalfordParticipant @davehalford22513]

I've run a 3/8" horizontal cutter in alloy at about 1/8" depth using a Centec 2, it didn't mind too much.

You don't want more than one tooth cutting at once especially with steel needing twice the power.

Don't forget the Centec 2 has the same size mast as the 2B, just shorter.

Hope the plate is black steel, otherwise it will banana as Howard says.

[Neil WyattModerator @neilwyatt]

Posted by SillyOldDuffer on 29/11/2017 11:31:57:

(in Watts per second)

Edit – just realised you mean Watt-seconds  not watts per second.

Neil

Edited By Neil Wyatt on 29/11/2017 20:46:20

[SillyOldDufferModerator @sillyoldduffer]

Posted by Neil Wyatt on 29/11/2017 20:44:37:

Posted by SillyOldDuffer on 29/11/2017 11:31:57:

(in Watts per second)

Edit – just realised you mean Watt-seconds not watts per second.

Neil

Edited By Neil Wyatt on 29/11/2017 20:46:20

Doh – good job there's an editor about to spot these blunders! I'm definitely past my 'Best Before Date' – yesterday I caught myself looking for teabags in the fridge…

[Ian Skeldon 2Participant @ianskeldon2]

Posted by SillyOldDuffer on 29/11/2017 21:58:08:

Posted by Neil Wyatt on 29/11/2017 20:44:37:

Posted by SillyOldDuffer on 29/11/2017 11:31:57:

(in Watts per second)

Edit – just realised you mean Watt-seconds not watts per second.

Neil

Edited By Neil Wyatt on 29/11/2017 20:46:20

Doh – good job there's an editor about to spot these blunders! I'm definitely past my 'Best Before Date' – yesterday I caught myself looking for teabags in the fridge…

That's NOT how you make iced tea !

[Neil WyattModerator @neilwyatt]

Posted by SillyOldDuffer on 29/11/2017 21:58:08:

Posted by Neil Wyatt on 29/11/2017 20:44:37:

Posted by SillyOldDuffer on 29/11/2017 11:31:57:

(in Watts per second)

Edit – just realised you mean Watt-seconds not watts per second.

Neil

Edited By Neil Wyatt on 29/11/2017 20:46:20

Doh – good job there's an editor about to spot these blunders! I'm definitely past my 'Best Before Date' – yesterday I caught myself looking for teabags in the fridge…

Look on the bright side, at least you remembered what you were looking for.

Neil

[not done it yetParticipant @notdoneityet]

You were not the only one to notice.

BTW, Watt seconds are properly called Joules. Watts is Joules/second.

Temperature was down to less than (K + 273) Celcius this last night. Everyone knows it was 'freezing' (below the freezing point of pure water). Best to keep simple SI units.

[SillyOldDufferModerator @sillyoldduffer]

Posted by not done it yet on 30/11/2017 06:29:10:

…

BTW, Watt seconds are properly called Joules. Watts is Joules/second.

 

… Best to keep simple SI units.

True! Unusually there was some method in my madness. I deliberately used Watt-Seconds because of the unit's fairly obvious relationship to the Kilowatt-Hour. Metric and Imperialist fanboys both are likely to understand kWh.  Shame I spoilt it all by making the Watts per Second mistake.  Ho hum.

3600000 Watt Seconds = 1kWh as per our electricity bills.
3.6MJ = 1kWh is less obvious unless you're familiar with SI.

Dave

 

Edited By SillyOldDuffer on 30/11/2017 09:56:37

[Neil WyattModerator @neilwyatt]

Posted by SillyOldDuffer on 30/11/2017 09:52:46:

3600000 Watt Seconds = 1kWh as per our electricity bills.
3.6MJ = 1kWh is less obvious unless you're familiar with SI

Somehow 15p for 3.6Megajoules sounds a better deal…

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