sfpm for shiny surface with carbide tools

DMF_TomB · Jan 27, 2017

i got some new to me facemills and notices when sfpm get above 700 doing light cuts on cast iron the surface finish gets shiny
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at edges dull for 1/2" till facemill warms up so i tried 850 sfpm and it gets surface more shiny closer to part edges.
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i am just asking anybody notice what sfpm do carbide machined surface go from dull to extra shiny surface ? i am assuming it is the chips are hotter and reason surface are shiny.
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obviously if facemill is throwing a lot of sparks it is going fast. basically shiny surface often happens just a little slower than when sparks start coming off facemill. inserts rated for up to 950 sfpm.

npok · Jan 28, 2017

IME, it's all about the heat generated at the edge + the material.

Have you tried running you finish pass dry? At a lower sfpm of course.

DMF_TomB · Jan 28, 2017

npok said:
IME, it's all about the heat generated at the edge + the material.

Have you tried running you finish pass dry? At a lower sfpm of course.

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i have run with and without coolant. no difference in finish usually.
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one facemill gives moderately shiny finish at 450 sfpm but the new one goes from dull to extra shiny when going from 450 to 850 sfpm, it is very noticeable. we have had it going 950 sfpm per salesman recommendations but 850 sfpm gives more stable tool life
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i have seen carbide tools on lathes do similar in surface goes from dull to shiny when a certain sfpm is reached. it will not happen if going slow. shiny surface is actually more smoother and shiny than most blanchard ground surfaces. as long as it passes .0003" flatness spec at over lap areas and edges i will be happy
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i was going to change another facemill to new style inserts but some wise guy bolted on facemill with red loctite on threads. 2 broken allen sockets and 3 broken allen wrenches later i gave up. might have to drill the facemill bolt out.

robert123 · Jan 28, 2017

If you heat the bolt with a torch hot enough to burn off the Loctite, it should come out pretty easily.

DMF_TomB · Jan 28, 2017

robert123 said:
If you heat the bolt with a torch hot enough to burn off the Loctite, it should come out pretty easily.

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the facemill bolted on tool holder is probably heat treated high strength steel. if i was not worried about annealing or loosing heat treatment it by using torch i would try the torch

Mark Rand · Jan 28, 2017

Loctite will lose its strength at about 250°C/480°F. That won't noticeably affect the temper of any steel. Stick it in the kitchen oven at that temperature for long enough to soak, then attack it with Allen keys, vise grips etc..

DMF_TomB · Jan 29, 2017

Mark Rand said:
Loctite will lose its strength at about 250°C/480°F. That won't noticeably affect the temper of any steel. Stick it in the kitchen oven at that temperature for long enough to soak, then attack it with Allen keys, vise grips etc..

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tool holders over 16" long and at work nothing but small toaster ovens for food. not for cooking loctite fumes. trusting the welder to use a torch on it ? maybe i trust machinist more to drill out the bolt and do less damage
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personally i use anti seez and not loctite when attaching facemill. i used impact wrench and busted 2 allen sockets and also broke 3 allen wrenches using cheater pipe and a hammer. not sure why anybody would use red permanent loctite to attach carbide insert facemill

adama · Jan 30, 2017

Put a bar of steel or punch in the bottom of the bolt and just hit it hard axially along the tool holder think 2lb hammer hard swings, but nothing crazzy. They always undo after that! Loctite does not make all that much difference, its the head - surface interface friction you can't over come!

ghost_rider · Jan 30, 2017

This has more to do with experience getting a good finish on a surface then anything. But carbide likes pressure. Either leave more material for a finish pass or speed up the spindle to get the desired effect. You cannot always go with the books recommended settings at times.

DMF_TomB · Jan 30, 2017

ghost_rider said:
This has more to do with experience getting a good finish on a surface then anything. But carbide likes pressure. Either leave more material for a finish pass or speed up the spindle to get the desired effect. You cannot always go with the books recommended settings at times.

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flatness tolerance of .0003" and more than .003" final pass will not make the tolerance. most programs have final pass of .0005" to .0010"
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depth of cut does not effect shiny surface although heavy depth of cut will cause sparks at higher sfpm cutting dry, shiny surface is mostly a cosmetic thing some would think surface was ground rather than milled

Matt_Maguire · Jan 30, 2017

DMF_TomB said:
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the facemill bolted on tool holder is probably heat treated high strength steel. if i was not worried about annealing or loosing heat treatment it by using torch i would try the torch

I wouldn't flinch at heating the capscrews up, just don't try to twist on them till back below 200-250 or so.

The tool steel for the better cutter bodies are all following the 5% chrome hot work tool steel recipes. You need to get north of 1100°F to be where the body was double tempered to start with. Even above 1200° it would take some time to drop properties much…

The insert pockets are expected to run near those temps under the insert edges before deforming quickly under load, and in general run a long time before fatigue shows its’ ugly face. Pretty good shit those H series are, loads better than the sewage the cap screws are made of.

If I had nothing else, I’d drop a washer over the capscrew & weld it up. Work my way around and put a 1/2” nut on top, then rinse & repeat. When finished the 1st screw would come out with a harbor freight 6” adjustable wrench.

Good luck,
Matt

DanielG · Jan 30, 2017

DMF_TomB said:
tool holders over 16" long and at work nothing but small toaster ovens for food. not for cooking loctite fumes. trusting the welder to use a torch on it ? maybe i trust machinist more to drill out the bolt and do less damage

You might pick up a cheap electric oven. They're very useful in the shop for un-Loctiting things, heating up parts/bearings, etc.

This is basically what I used, but newer. $20 at Walmart.
https://www.walmart.com/ip/Mainstays-20-Pound-Turkey-Roaster-with-High-Dome-Lid-14-Quart-Black/53986439

DMF_TomB · Jan 31, 2017

DanielG said:
You might pick up a cheap electric oven. They're very useful in the shop for un-Loctiting things, heating up parts/bearings, etc.

This is basically what I used, but newer. $20 at Walmart.
https://www.walmart.com/ip/Mainstays-20-Pound-Turkey-Roaster-with-High-Dome-Lid-14-Quart-Black/53986439

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i can ask maintenance people. they often heat parts for shrink fitting on. welder might have welding rod oven too. i will ask if they can remove the stuck screw. as cnc operator i do not have the tools to remove stuck screws as when a lean department that just means you do not have any tools beyond what is expected to need most of the time.

DMF_TomB · Oct 15, 2017

shiny milling cast iron as picture of reflection of indicator shows
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gets shiny roughly 600 to 950 sfpm but how many feet it does before its dull and not shiny is the tricky part.

LKeithR · Oct 15, 2017

Matt_Maguire said:
...I wouldn't flinch at heating the capscrews up, just don't try to twist on them till back below 200-250 or so....

Yup, small oxy-acetylene torch with a small tip--concentrate the heat on the head only. It can get damn near red hot--which will drive
the heat down the length of the capscrew and loosen the loctite--without doing any damage to the body of the cutter. A couple of heat
and cool cycles should take care of the problem...

cwtoyota · Oct 15, 2017

DMF_TomB said:
shiny milling cast iron as picture of reflection of indicator shows
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gets shiny roughly 600 to 950 sfpm but how many feet it does before its dull and not shiny is the tricky part.

I don't know the exact point where it starts to take a shine, but this is the same polished finish in mild steel.
The mirror sitting on the block is a 38mm square to give an idea of scale.

This block is flat and parallel within .0003 inch and "floats" on the surface plate.
It was cut with a 3" SDMT face mill with 6 flutes at a pretty high surface speed.

BSCustoms · Oct 16, 2017

The 'shinyness' often has to do with burnishing the surface. When you get it hot enough, whether through heavy cut or increased SFPM, you get plastic deformation. Some of this goes away in the chip some gets 'mushed' back into the surface and wiped over. Look into the idea of wiper inserts.

lakey0 · Oct 16, 2017

BSCustoms said:
Look into the idea of wiper inserts.

Just started using wiper insert in our face mill, so far so good. Seems like a good option in rigid setups.

DMF_TomB · Oct 16, 2017

BSCustoms said:
The 'shinyness' often has to do with burnishing the surface. When you get it hot enough, whether through heavy cut or increased SFPM, you get plastic deformation. Some of this goes away in the chip some gets 'mushed' back into the surface and wiped over. Look into the idea of wiper inserts.

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i use other mills with wipers these do not have wipers. these inserts dull fast with heavy cut over .003 DOC unless slowed down, literally can go shiny to dull in less than 3 feet. salesman recommendations we tried many times and usually inserts dull in a few feet. the range on cast iron is 330 -820 sfpm and .003 to .010" ipt
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at 820 sfpm .003 ipt they dont last long. 700 sfpm .003 ipt or less they last longer and more important surface waviness is usually more than .0003" if feed is faster. also semi finish heavier than .003 DOC the insert life is short i find they last longer 500 sfpm <.005 ipt, its taking some testing to find sfpm and ipt for inserts to last more than 45 minutes and give .0003 or less waviness. salesman recommendations lucky inserts lasted 10 minutes
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they will still cut longer but without the shiny surface. also when dull they sometimes give a shiny surface with a vibration pattern waviness which can come and go randomly. many a time i have recut with new inserts and everything is shiny low waviness again.
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yes at slower 600 sfpm often its dull for first 1/4" near edge till inserts warmup then shiny rest of the way. with coolant the transition is at higher sfpm. with coolant can go faster but part often distorts from temp changes even though coolant is temperature control there is evaporation cooling causing problems. so we are trying with and without coolant but neither is perfect

DMF_TomB · Oct 16, 2017

Matt_Maguire said:
I wouldn't flinch at heating the capscrews up, just don't try to twist on them till back below 200-250 or so.

The tool steel for the better cutter bodies are all following the 5% chrome hot work tool steel recipes. You need to get north of 1100°F to be where the body was double tempered to start with. Even above 1200° it would take some time to drop properties much…

The insert pockets are expected to run near those temps under the insert edges before deforming quickly under load, and in general run a long time before fatigue shows its’ ugly face. Pretty good shit those H series are, loads better than the sewage the cap screws are made of.

If I had nothing else, I’d drop a washer over the capscrew & weld it up. Work my way around and put a 1/2” nut on top, then rinse & repeat. When finished the 1st screw would come out with a harbor freight 6” adjustable wrench.

Good luck,
Matt

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i got screw out long ago i just put it in a dry ice freezer then used a impact wrench. came off in about a minute

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