# What Did I Do Wrong?



## lcorley (Jul 19, 2015)

I just got my PM25MV up and running.
My 1st project was this wrench for removing wire wheels from my angle grinder.
I started with a 2 1/2 wide 1/4 hot rolled strip.
I cut the handle to rough size with a plasma cutter and roughed out the notch with a bandsaw.
I clamped the wrench on edge in my vise and milled the handles smooth.
I didn't go well.  I used a 1/2" mill at 150 rpm.
I dulled 2 of them on the ends.
The mills were HSS from HF
www.harborfreight.com/20-piece-titanium-nitrade-coated-end-mill-set-5947.html

I though I might be turning too slow so I looked it up.
I was, so I tried a 9/16 mill at 700 rpm, dulling it as well.
I cut the mouth with the wrench clamped flat in the vise.
I used the 9/16 mill at 700 rpm.  It worked better.




Can anybody give me some advice here?
Thanks in advance.

Leon


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## JimDawson (Jul 19, 2015)

I think you should have been using the angle grinder to get past the hard scale left by the plasma torch, then mill if needed.  The proof of this is milling the band saw cut vs. the plasma cut.

I've had pretty good luck with the HF end mills.  I wait for the 20% off coupon to buy them. 

700 RPM seems a bit high for a 9/16 in steel unless you are using flood coolant.


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## RJSakowski (Jul 19, 2015)

lcorley said:


> I just got my PM25MV up and running.
> My 1st project was this wrench for removing wire wheels from my angle grinder.
> I started with a 2 1/2 wide 1/4 hot rolled strip.
> I cut the handle to rough size with a plasma cutter and roughed out the notch with a bandsaw.
> ...



Hot rolled steel has an oxide coat that is hard on HSS tooling.  I remove it first, either by abrasion (grinding, sanding, etc.) or chemically (muriatic acid).
The plasma cut edges may have hardened.  There is enough carbon in hot rolled to harden the steel and the rapid cooling as the torch moves away is sufficient to quench the steel.  I have no experience with plasma cutting but this certainly happens with flame cutting.  I grind the cut edges back to parent material before machining.  You could also use carbide.
I also don't trust anything with a cutting edge from HF.

Bob


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## seasicksteve (Jul 19, 2015)

Make sure you are turning the spindle in the right direction. Not trying to be smart azz it happens


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## lcorley (Jul 20, 2015)

Thanks for the comments.
Here's a pic of the worn end mills.



I plan on replacing the 1/2" with carbide.

Do you reckon the interrupted cutting on the edge contributed?

Leon


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## JimDawson (Jul 20, 2015)

Interrupted cutting with an end mill does not hurt it at all, by their nature the cut is always interrupted except when plunging..

I'm pretty sure what killed the end mills is the very hard scale left by the plasma torch. 
.
.


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## Doubleeboy (Jul 20, 2015)

When I have to machine scaly material I try and use a flycutter if I can to get thru the scale.  Pretty cheap to touch up a HSS bit as opposed to trashing an endmill. 

michael


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## lcorley (Jul 22, 2015)

Would a flycutter have worked on the 1/4" edge of the wrench?
I thought they were for large areas.

regards,
Leon


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## chips&more (Jul 22, 2015)

The skin on all metals must be considered before machining it. Hot rolled and any metal cut with high temperature will leave unknown metal surface conditions that can ruin cutters. You either cut underneath the skin of the metal or remove the skin first (typically with abrasion)…Good Luck, Dave.


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## Wreck™Wreck (Jul 26, 2015)

lcorley said:


> Thanks for the comments.
> 
> 
> I plan on replacing the 1/2" with carbide.


You want to use carbide tooling in such an unstable machine? Good luck.
I would not try that in a fairly recent Bridgeport knee mill let alone a hobby machine, save your money and stick with HSS tooling, you can buy 5 or 6 HSS endmills for the cost of the one carbide tool that you will destroy immediately.
Your Mileage May Vary of course


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## Bill C. (Jul 26, 2015)

Fly cutters are used to cut large areas like a face end mill.  If the chips are dark blue then the speed is to fast.  I have used HRS and I know its used for weldments all the time.  I've used angle iron to make small angle plates after cleaning the outer surfaces of scale.

I never used a coated end mill that I can recall. Not sure why they are coated.  I would ask HF to replace the end mills, can't hurt to ask.


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## gaston (Jul 26, 2015)

looks like you took too light of a cut and didn't get thru the plasma affected zone. I have done the same thinking I was being easy on the tool.
you need to cut deeper and slower till you see how it reacts. As for not useing carbide in a hobby machine, I think thats BS. I have used carbide end mills in a drill press many times to "fix a screw up"to cut hard material that ate a drill or tap and never hurt one.(be careful as they are easy to chip).  Can't beat carbide tooling for dealing with hard stuff.


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