Newbie- Need Help with Coolant Issue!

[Chaps]

I am currently using a Sieg X2 mill converted to CNC. I built a project which required milling 1/2" steel plate. I started with a spray bottle of coolant to keep cutter cool then bought a mist unit from Little Machine Shop. I am considering a face mill 2 1/2" or 3" from EBAY (Sandvik). Some of the threads indicate that with the belt conversion (I have already completed) I could use a 3" with shallow cuts. I looked at forums on coolant. Now I am totally confused

[It seems everyone has different advice:
Don't use coolant--shocks the cutter ruins life of tool.
Do use coolant but use a mister only.
Don't use mist use flood coolant.
Use coolant on steel but not on aluminum.
Would someone please condense all these issues into something simple enough for a newby to understand?????

[ctate2000]

IMHO:

In theory you can machine all materials without coolant. Coolant aides efficiency more than anything. Coolant does several things to aide the machining process:

1. It cools. By removing the heat produce during the chip formation process you prevent the material from becoming ductile ahead of the shear zone.

2. Lubricity. The lubricating properties reduce heat from friction and improve tool life.

3. Washes chips away from the work zone.

In short the coolant allows you go faster. There is a lot of research out there about the role of coolants in machining.

[Shotout]

Originally Posted by Chaps I am currently using a Sieg X2 mill converted to CNC. I built a project which required milling 1/2" steel plate. I started with a spray bottle of coolant to keep cutter cool then bought a mist unit from Little Machine Shop. I am considering a face mill 2 1/2" or 3" from EBAY (Sandvik). Some of the threads indicate that with the belt conversion (I have already completed) I could use a 3" with shallow cuts. I looked at forums on coolant. Now I am totally confused [It seems everyone has different advice: Don't use coolant--shocks the cutter ruins life of tool. Do use coolant but use a mister only. Don't use mist use flood coolant. Use coolant on steel but not on aluminum. Would someone please condense all these issues into something simple enough for a newby to understand?????

ctate2000 broke down what coolant does pretty well. As was stated there is a lot research out there and it is a complicated subject at times.

To break down your examples:
Thermal shock- Inconsistent coolant flow to the cutting edge from a variety of causes allow the cutter to heat up to a point that when quenched in a coolant the edges will deteriorate. Some materials can't be quenched after they reach a certain temperature as they shatter or micro fracture such as carbides. HSS and M42 have thermal ranges as well. This shouldn't be a concern with your machine.

Mist coolant only- for traditional machining techniques (cutter engagement, speeds and feeds) a mister will usually work well just so long as it is always directed at the cutting edge and isn't forcing chips back into the cut. With your machine you'll probably be cutting even lighter than that so it should work well.

Flood coolant- allows faster cutting for the reasons stated by ctate2000, also in more aggressive cutting conditions a mister might not get coolant to the cutting edge due to the cutters temperature boiling off the water in the mist, like a vapor lock. You shouldn't have this issue with your machine. If you have a full enclosure around your machine you'll usually be OK just flooding it. If not your cutter may sling coolant everywhere with a gusto when you are using a good speed range for the cutter diameter ranges that machine can handle. This holds true in a mist system too but with a much lower volume of coolant. I'd say containment and collection would be your only worry on your machine.

Coolant per material- In steel or aluminum the need for coolant is in relation to the way the material is being cut, not an either or. I generally use coolant on aluminum to prevent chip welding, improve surface finish etc. Even on the conventional mills I would use WD-40 when side milling and to finish fly cutting/facing even if I rough cut dry. On the cnc mills, well lets just say I have a need for speed and couldn't machine without it. For steels it comes down to what type of steel and how machining effects it (carbon content alloy content). If you are going slower, using traditional methods coolant can be an either or proposition but often will impart a better surface finish for finishing cuts.

Easy solution, use air. On the conventional mills I generally will pull the pickup tube out of the coolant reservoir and just let it be a low pressure forced air system. I can keep the chips clear, the low pressure air helps dissipate heat through convection cooling and if needed on finish cuts an acid brush dipped in an appropriate cutting oil allows me to paint a little oil where needed and keeps my fingers OEM length and you don't end up with a mess to clean up at the end of the day.

For you Sandvik cutter, providing you can achieve the SFM and chip load range of the insert, using a proper DOC (doubtful) you'll get a clean cut with or without coolant in low carbon steel, if you aren't running it as the manufacture suggested then either way your surface finish will be less than what the cutter should provide. Keep in mind insert geometry dictates a minimal DOC too and not leaving enough material to cut on a finish pass can also impart a lesser quality surface finish as will running to slow or too fast. With smaller industrial use machines they often can't provide the power required to run larger face mills with good results. Fly cutters however are great on smaller machines, they are cheap to buy and if you have access to a lathe they are also easy to make, lathe tool bits used in them are cheap and available in different geometries that allow you to simply change a bit when changing material and they can be resharpened on a pedestal grinder in the shop. A quick google search found the specs for that machine state the max face mill is 30mm, about 1.2". Personally I wouldn't subject that machine to the wt of a 3" face mill, but a fly cutter yeah I can see that working well. I would caution you though, the specs state 30mm diameter max. Trust the engineers that designed and tested that machine to know what it can handle and provide a useful life. Anything over that, well as the cutting forces move out radially from the center of the spindle it is going to increase the load on the spindle, think lever, which means increased load on bearings, bushings and the Z column. I'd hate to know you messed up your machine because you didn't know to factor these things in.

My opinion at least.

[Chaps]

Thanks ctate200 and Shotout. Much more concise information. I have already experienced finish problems with a 1" hogger. I was making the final pass VERY light and getting some areas that were great and some less than satisfactory. I increased the depth of final cut and it has greately improved the finish. Thanks for that information.

Is "chip welding" the problem I keep encountering on aluminum when it cuts great then becomes "sticky" and finally melts onto my cutter????? I tried coolant on aluminum also and it greatly reduced that problem. But other videos I have watched show full thickness cuts of up to 1" without coolant and no problem.

Aren't Newby's a royal pain??????

[wendtmk]

You probably oughtn't be trying to do your finish passes with the "hogger." That endmill is typically used for removing copious quantities of metal from the work piece, not necessarily for giving you a nice finish.

mark

[Chaps]

Thanks for the tip. I guess I'll have to wait til my face mill arrives. That was a good lesson learned.