Thread: Narrow slots - Woodruff ? Slottting Endmill ? Other ?

I regularly break narrow slottcutting 2 tooth end mills - anything less than 6mm seems in danger of my hamfistedness. I have also broken a few narrow 4 tooth end mills.

Mill is Rong Fu 30 with a 2HP motor, hand cranked & no DRO. Material is usually black bar or Aluminium.

Was wondering about turning work sideways and using a woodruff cutter - have done some googling but not finding any good pages to help me understand whether or not this is a viable idea.

Are there 3 options for cutting a slot ?

2 tooth end mill
woodruff cutter
T-slot cutter - different to a woodruff cutter ?

Or maybe slow down a bit and try not to break the 2 tooth end mills ?

My best slots have been started with a 2 tooth slotcutting endmill and then finished by shaving the edges with a smaller 4 tooth end mill. My attempts with the 2 tooth mills are far better as the diameter gets larger.

Any good web pages / books that I should read on this ?

Have got some siver steel and will have a go at making making one of these from Harold Hall's website http://www.homews.co.uk/TSlotCut01.pdf

Bill

Hi Bill, I think I've a few of those T slotters that I got somewhere, yours if you want to try one. What width cut are you wanting to make???
Kryn

Originally Posted by KBs PensNmore

Hi Bill, I think I've a few of those T slotters that I got somewhere, yours if you want to try one. What width cut are you wanting to make???
Kryn

Thanks for the offer Kryn, there is no particular size - I've simply noticed that I break lots of narrow slotcutters compared to thicker ones.

Am chasing a better understanding of what the 3 types of cutters can and cannot do and when to use them, probably better for me to do a bit more reading before mangling any more cutters.

Would like to have a go at making one just for the fun of it, should be okay to use in aluminium.

What did you use the T cutters for and would you use them instead of an end mill for any particular slotting jobs ?

My most recent failure was 6mm slot in the qctp toolholders and was thinking if I tip the blank on its side and use a T-slot / woodruff cutter that would be less likely to break than a skinny end mill.

Bill

The only differences i have ever noted between t slot cutters and woodruff cutters is that t slot cutters more often than not have staggered teeth to deal with the bigger chip load, they also can have a thicker stem than a woodruff cutter which by the nature of woodruff keys have to be able to plunge quite deep.

For narrow slots you perhaps need to be using a slitting saw (making an arbor is a simple lathe job). T slot cutters or woodruff key cutters will work but are limited in the depth of slot that you can produce.

Small endmills will break though if they are overloaded. You should be using a high rpm and limiting your depth to around 1/2 to 1 diameter of the cutter. If you can use coolant or even a vacuum cleaner to keep the cut clear of chips that will also help.

Michael

Originally Posted by Michael G

For narrow slots you perhaps need to be using a slitting saw (making an arbor is a simple lathe job). T slot cutters or woodruff key cutters will work but are limited in the depth of slot that you can produce.

Small endmills will break though if they are overloaded. You should be using a high rpm and limiting your depth to around 1/2 to 1 diameter of the cutter. If you can use coolant or even a vacuum cleaner to keep the cut clear of chips that will also help.

Michael

Half diameter DOC max is what I was taught for a full width cut.

For small cutters you need a high spindle speed. The formula to work it out is well known - google it. Then you need to use the proper feed per tooth to maximise cutter life.

On an RF-30 without power feed you're pushing the proverbial faeces up a steep slope.

Flip side - IF your spindle speed goes slow enough AND you aren't cutting a blind slot OR a ramped runout either end is acceptable, a slitting saw is the way to go. You can plunge cut with them fine, you'll just get a ramp either end of the cut.

Given a choice between a 3mm slot drill or smaller and a slitting saw on a slot starting & ending in air I'll always go for the slitting saw. Otherwise high RPM and flood coolant to get the chips out.

PDW

Originally Posted by steamingbill

What did you use the T cutters for and would you use them instead of an end mill for any particular slotting jobs ? Bill

Bill, I got them as a bulk lot, along with a heap of tapered round ended milling cutters. I think from memory I used one when I started to make a cast iron angle table with 3 T slots, had about 25 -30 mm to go to finish it, when the X2 mill cacked itself AGAIN, never did get to finish it off, hopefully by the end of the year it'll get done.
I've not done much milling work yet, apart from the time I had the X2 POS, for about 18 months, never used one prior to then.
If you need it, let me know and I'll drop it in the post to you.
Kryn

Did some googling re differences woodruff vs t slot, might be of interest to others.

T-slot vs Woodruff cutter

Need help with key way cutter/saw type geometry feeds and speeds in 6061-T6

https://www.polytechforum.com/metalw...er-162784-.htm

Bill

4-flute cutters are bad juju for slotting. Avoid except where absolutely necessary.

Do literally anything in your power to avoid manual slotting under 6mm. Power feed improves things slightly, might get you down to 4mm.

Use compressed air blast + vacuum for chip clearance wherever possible.

As others have said, if you can rough out the slot using a slitting saw or t-slot cutter, any material you can remove is a positive thing. The biggest problem with slotting is chip evacuation, and saws and t-slot/woodruff cutters excel at chip evacuation by their nature.

Originally Posted by steamingbill

Or maybe slow down a bit and try not to break the 2 tooth end mills ?

Bill

Bill what RPM are you using? A machine like that will probably be nearly flat out spinning anything under 5 mm even is steel.

If you're breaking tools when slotting you should look at increasing your RPM, and reducing your DOC and feed rate. Particularly in aluminium ensure the chips are being cleared from the slot. It's easy for the tool to get loaded up with chips and that alone can snap small bits.

Pete,

My top speed on the RF30 is a tad over 2000 rpm

For a 6mm slot cutter I calculated 1600 rpm, in his books Harold Hall recommended 1000 rpm and elsewhere I have seen the rpm for TIN coated cutters as being HSS + 10%.

I tried various speeds 1000, 1300 and 1540 and tried various DOC between 1.5 and 3mm. No matter what I do with the narrow cutters it never feels or sounds right ..... and they snap quite easily ..... yet when I did a 3/8" slot just beforehand the cutter just sort of whispers along leaves a tidy clean cut slot no worries.

Maybe I am blunting the smaller cutters with my first cut and from then on its all downhill

I just gotta practice I think. ......

Bill

For small cutters, chipload is everything. You generally want to aim for a 0.02mm chipload in steel - which means for a 2 flute slot drill at 1000rpm, your feed rate is going to be 40mm/min. That means you need turn your feed screw one revolution every 3.75 seconds, very evenly. If you accelerate even just a little, you'll suddenly be giving the cutter a much larger instantaneous chipload, and that's what will break it. If the chip from the last cut hasn't cleared and gets recut, suddenly you're giving the cutter double chipload. Small cutters in slots get deflected, and when they get deflected they bite, and suck themselves into the part.

To successfully slot you need to balance all of these factors - spindle speed, feedrate/chipload, chip clearance - and that's just to avoid breaking the cutter.

All told, if you take a methodical and practical approach to getting the job done, you'll be ok. Anything is possible with sufficient attention to detail.

As a rule of thumb (in mild steel) I use 30 m/min for HSS and 100 m/min for titanium. For a 5 mm cutter that equates to just under 2000 rpm. 1000 rpm is way too slow. Without power feed, as mentioned above, any variation in feed rate will exaggerate the chipload, and when it exceeds the cutter's capacity it will snap. 3 mm DOC for a 5 mm cutter is also rather ambitious for your setup I'd suggest.

Increase your rpm, decrease your DOC and ensure your feed rate is both appropriate and consistent. When slotting there can be a tendency to re-cut chips, so make sure they are properly cleared from the slot, use low pressure air if you need to. I have some Noga mini-cools that are handy for that. When cutting aluminium, chip clearance can be a particular problem in my experience as everything is happening much faster. If the aluminium chips aren't cleared they can weld to the cutter, and I've snapped even quite a decent sized end mill from not clearing the chips when I had to plunge down into gummy aluminium and didn't pre-drill.

I think a common error is to slow everything down thinking that will help, but many times that will actually aggravate the situation. A small cutter needs to be spun fast or the chipload will become too high (ie it will snap). Similarly, too low a feed rate will cause the cutter to rub and it will dull. You should be able to see if your cutter is dull as you suggest; a sharp cutter will be, well, sharp.

If you want to practice, then reduce your DOC way down, 0.5 mm or so. That way even if you don't get things right the chances are that the deflection won't be enough to actually break the tool and you can experiment with different variables. You didn't say what you're using for cutting oil or coolant, but play with variables at a low DOC, watch your cutter and chips, and it should become obvious when the cutter is working well.

Finally, I'm not sure exactly what you're referring to when talking about slotting "black bar". If you mean hot rolled mild steel then that's one thing, but many people will take that to be a piece of reo or some other crap they got from the scrappy or found on the road somewhere and then they expect to get good results when machining it. If the pedigree of the material being machined isn't known, there's not much chance of being able to get consistent results when machining it. Obviously there are many times when we have a job where we need to machine something and it doesn't need to be pretty or particularly strong. However generally speaking you will want to know a bit about the material you're dealing with. That's the fuel for the engine, and if rubbish fuel is used, the chances are the results will be equally rubbish. When experimenting you want to eliminate as many variables as you can, so you can focus on changing just one thing at a time and seeing what happens. With small cutters on a manual machine the margin for error becomes quite small, so I'd suggest trying to get the odds in favour.