Various questions about X2 mill

[shooter123456]

Ive been trying something new recently by CNCing my X2 mill and it has lead me to a lot of things I don't understand or need to improve.

Motor Questions:

How can I tell if the brushes need to be replaced? I know its lost steam recently. Around February last year I drilled a 3/4" hole in 303 stainless up from a 1/2" hole. It was slow going but it didn't stall. Just recently, I tried to do the same thing in 6061 and it would stall out almost immediately.

My motor is advertised as 4/5 HP, but everything I can find says it is running at 350W. 4/5 HP would be 595W, and even at 110V and 4.5A, thats only 495W. How can I figure out how much power it is actually drawing?

I have read about people replacing their controllers to improve speed and torque. The boards I have found are about $75 shipped. I have found a lot of treadmills with 2HP+ motors for around there. Any reason I should do one of these over the other?

Spindle/Tool Holder Questions:

I am going to be using TTS holders with a .75" collet. What amount of spindle runout is expected/reasonable? I am all about chasing small numbers, but I need to know when I am wasting my time.

Since the holders will be tightening against the spindle face, should I face that? Anything wrong with tightening a lathe tool into the vise and just cutting it with that?

Several miscellaneous questions:

Is it safe to use loctite on gib screws? I find that even with the nuts locked down, nothing stays tight for more than a day or two worth of machining.

Any tips on taking light cuts in 4140 on the lathe while still getting a good surface finish? When turning at about 600 RPM near .750" diameter with a 3/8" insert tool, I get a perfect finish with .0015" cut depth, but anything less than that and it comes out very rough. I haven't been able to get HSS to cut it well.

Any help you guys can offer is greatly appreciated.

 

[royesses]

Unplug the mill and remove the brushes. Look at the surface and check the length. New brushes are about .590" long. There should be no deep scratches or grooves on them. It would be good to change them when they get down to about .200" or so. I use canned air in one brush hole and a vacuum on the other to get as much dust as possible out of the motor. I like to give new brushes a concave shape to get them run in a little quicker. It is not uncommon to have less power with new brushes until they form to the surface of the commutator and have full contact. Use the old brushes as a guide for the radius to make on the new brushes. I can't help on the cnc conversion but someone on the forum will give you answers. I use blue loctite on my gib screws with no ill effects. I have not cut 4140 so I can't give any info on that.

Roy

 

[Wreck™Wreck]

Any tips on taking light cuts in 4140 on the lathe while still getting a good surface finish? When turning at about 600 RPM near .750" diameter with a 3/8" insert tool, I get a perfect finish with .0015" cut depth, but anything less than that and it comes out very rough. I haven't been able to get HSS to cut it well.

Any help you guys can offer is greatly appreciated.

Way to slow, 2000-2500 Rpm's would produce a much better surface finish on a diameter of that size with carbide, shoot for 300 SFM or so, with coated inserts as high as 600 SFM.

 

[shooter123456]

Way to slow, 2000-2500 Rpm's would produce a much better surface finish on a diameter of that size with carbide, shoot for 300 SFM or so, with coated inserts as high as 600 SFM.

I should have mentioned, I tried running it as fast as 1500 rpm and the result was similar. Anything under .0015 and the finish went to hell. In the past, the lighter cuts produced the best finish, but with 4140 in particular, I can't seem to cut well under that depth.

 

[Bob Korves]

4140 work hardens very easily, leaving a hard and tough skin. The only real answer is to not take light cuts, but to always make sure your tool is digging in under the harder surface. We are talking mill here, so make sure that the chip load is also deep enough to get under the "skin." When working up to a finish cut, have your second to the last cut no less that .010" from the final size, and then cut it all in one pass, simply plan that the cut will be the final cut, and then run with it.

 

[mikey]

Spindle/Tool Holder Questions:

I am going to be using TTS holders with a .75" collet. What amount of spindle runout is expected/reasonable? I am all about chasing small numbers, but I need to know when I am wasting my time.

Since the holders will be tightening against the spindle face, should I face that? Anything wrong with tightening a lathe tool into the vise and just cutting it with that?

Any tips on taking light cuts in 4140 on the lathe while still getting a good surface finish? When turning at about 600 RPM near .750" diameter with a 3/8" insert tool, I get a perfect finish with .0015" cut depth, but anything less than that and it comes out very rough. I haven't been able to get HSS to cut it well.

I honestly don't know of anyone who has faced the spindle nose before using the TTS system. I suppose you could, though. However, I would be more concerned with how accurate the spindle is in the first place. Have you measured TIR with the current spindle and bearings? That is really what determines how accurate the system will be; well, that plus the stacking tolerances you get from mounting things in a collet. To my knowledge, Tormach doesn't state what the run out of their tooling is anywhere on their site. I use the TTS system and I like it but I have not really measured the run out of the tooling yet. My spindle run out is under 0.0001" and if the run out of the tools is greater than 0.0005" I would be surprised, but don't hold me to that because I am guessing.

As for cutting 4140 in the lathe with carbide, what is the nose radius of your cutter and does it have a chip breaker? Aside from the speed issue that Wreck addressed, if you are taking a cut less than the nose radius + maybe 0.005 - 0.010", you may have chatter and finishing issues. The reason is simple; if the nose radius is unsupported in the cut then tangential and radial forces increase until your depth of cut exceeds the nose radius, at which time radial forces depend on the lead angle of the tool holder. At very light depths of cut, your tool is deflecting and you will have finishing issues. When you use a chip breaker, you need both speed and depth of cut. The insert manufacturer will usually give you a recommended depth of cut for that insert; I've found that listening to them is a good idea.

Then there is the problem Bob pointed out - work hardening. Light cuts will run on top of a hardened layer and you have to cut under it to get a good finish.

You might want to try roughing heavy at lower speeds to get close to size, then switch to an insert with a smaller nose radius that you can bury in the cut to finish and do it at higher speed. 4140 is not the easiest stuff to cut. I have better luck using HSS to finish but my tool geometry is modified to work with it.

 

[shooter123456]

4140 work hardens very easily, leaving a hard and tough skin. The only real answer is to not take light cuts, but to always make sure your tool is digging in under the harder surface. We are talking mill here, so make sure that the chip load is also deep enough to get under the "skin." When working up to a finish cut, have your second to the last cut no less that .010" from the final size, and then cut it all in one pass, simply plan that the cut will be the final cut, and then run with it.

Thank you for your response. I thought I specified that I was turning the 4140 on the lathe, though I think it all still applies.

 

[shooter123456]

I honestly don't know of anyone who has faced the spindle nose before using the TTS system. I suppose you could, though. However, I would be more concerned with how accurate the spindle is in the first place. Have you measured TIR with the current spindle and bearings? That is really what determines how accurate the system will be; well, that plus the stacking tolerances you get from mounting things in a collet. To my knowledge, Tormach doesn't state what the run out of their tooling is anywhere on their site. I use the TTS system and I like it but I have not really measured the run out of the tooling yet. My spindle run out is under 0.0001" and if the run out of the tools is greater than 0.0005" I would be surprised, but don't hold me to that because I am guessing.

As for cutting 4140 in the lathe with carbide, what is the nose radius of your cutter and does it have a chip breaker? Aside from the speed issue that Wreck addressed, if you are taking a cut less than the nose radius + maybe 0.005 - 0.010", you may have chatter and finishing issues. The reason is simple; if the nose radius is unsupported in the cut then tangential and radial forces increase until your depth of cut exceeds the nose radius, at which time radial forces depend on the lead angle of the tool holder. At very light depths of cut, your tool is deflecting and you will have finishing issues. When you use a chip breaker, you need both speed and depth of cut. The insert manufacturer will usually give you a recommended depth of cut for that insert; I've found that listening to them is a good idea.

Then there is the problem Bob pointed out - work hardening. Light cuts will run on top of a hardened layer and you have to cut under it to get a good finish.

You might want to try roughing heavy at lower speeds to get close to size, then switch to an insert with a smaller nose radius that you can bury in the cut to finish and do it at higher speed. 4140 is not the easiest stuff to cut. I have better luck using HSS to finish but my tool geometry is modified to work with it.

I am using the El Cheapo 3/8" insert tools, not sure what the nose radius is and I dont think it came with any manufacturers recommemdations. I'll look into some better tools with a smaller nose radius. I tried grinding HSS tools for it but had no luck. Ive been able to get very nice surfaces in aluminum, 01, and 303 stainless but the 4140 not so much.

 

[mikey]

4140 is considered a "free machining" alloy steel that is semi-hard in the annealed state, the way you buy it. It doesn't take much to form a superficial harder layer when cutting this stuff; your tool has to be continually cutting to work with this stuff. You may find that brazed carbide works better for you when cutting 4140 but keep the tool sharp. 4140 also doesn't finish that well at low speeds so I usually use a HSS tool ground to work with this stuff and take several light finish passes at the highest speed my lathe will go. I don't get a mirror finish with this stuff but I do get a nice satin finish similar to that of 1144.

You will find that even cheap tool holders will work well if the insert is tailored to the material you're cutting. I would suggest you download the catalog of some major insert maker and take a good hard look at the technical section where they discuss grades, coatings, nose radius and so on. The best info I found was the Circle Machine catalog but you'll have to look for it. Widia took them over and the Widia catalog sucks. If you're going to use inserts then you have to know how to use them properly and you really need a high speed lathe. Otherwise, learn to sharpen brazed carbide tools or HSS tools - you'll have better results.

If you want to grind a HSS tool that will cut this stuff, I suggest you use side and end relief angles of 12 degrees, side rake about 18-20 degrees and back rake at 15 degrees or so. These values are not arbitrary. The relief angles are conservative to maintain edge strength. The side rake is slightly aggressive to improve chip flow and reduce cutting temperatures. Back rake is also slightly aggressive to reduce temps but it also improves finishes. I suggest a nose radius of about 1/32". For 4140, I suggest you use an 8% cobalt blank to handle the higher temps encountered in the cut.

When cutting this stuff with HSS, do not dwell in the cut - use power feed - and use sulfur-based cutting fluid. Cutting speeds are 70-200 but this is ambitious. I suggest you use 50-60 sfm for roughing; for a 1" diameter piece, you would use about 200 rpm to rough. For finishing, I suggest you take light cuts, somewhere around 0.005" depth of cut, at the highest speed your lathe will go and use a higher lead angle with your tool (angle the side edge more toward the tailstock than usual). Done this way, 4140 finishes nicely.

Hope this helps. If not, ask, and one of us will clarify.

 

[shooter123456]

4140 is considered a "free machining" alloy steel that is semi-hard in the annealed state, the way you buy it. It doesn't take much to form a superficial harder layer when cutting this stuff; your tool has to be continually cutting to work with this stuff. You may find that brazed carbide works better for you when cutting 4140 but keep the tool sharp. 4140 also doesn't finish that well at low speeds so I usually use a HSS tool ground to work with this stuff and take several light finish passes at the highest speed my lathe will go. I don't get a mirror finish with this stuff but I do get a nice satin finish similar to that of 1144.

You will find that even cheap tool holders will work well if the insert is tailored to the material you're cutting. I would suggest you download the catalog of some major insert maker and take a good hard look at the technical section where they discuss grades, coatings, nose radius and so on. The best info I found was the Circle Machine catalog but you'll have to look for it. Widia took them over and the Widia catalog sucks. If you're going to use inserts then you have to know how to use them properly and you really need a high speed lathe. Otherwise, learn to sharpen brazed carbide tools or HSS tools - you'll have better results.

If you want to grind a HSS tool that will cut this stuff, I suggest you use side and end relief angles of 12 degrees, side rake about 18-20 degrees and back rake at 15 degrees or so. These values are not arbitrary. The relief angles are conservative to maintain edge strength. The side rake is slightly aggressive to improve chip flow and reduce cutting temperatures. Back rake is also slightly aggressive to reduce temps but it also improves finishes. I suggest a nose radius of about 1/32". For 4140, I suggest you use an 8% cobalt blank to handle the higher temps encountered in the cut.

When cutting this stuff with HSS, do not dwell in the cut - use power feed - and use sulfur-based cutting fluid. Cutting speeds are 70-200 but this is ambitious. I suggest you use 50-60 sfm for roughing; for a 1" diameter piece, you would use about 200 rpm to rough. For finishing, I suggest you take light cuts, somewhere around 0.005" depth of cut, at the highest speed your lathe will go and use a higher lead angle with your tool (angle the side edge more toward the tailstock than usual). Done this way, 4140 finishes nicely.

Hope this helps. If not, ask, and one of us will clarify.

A lot of great information here. Thank you for your help. I will look at the tech section of the insert maker catalogs.

You said: For finishing, I suggest you take light cuts, somewhere around 0.005" depth of cut, at the highest speed your lathe will go and use a higher lead angle with your tool (angle the side edge more toward the tailstock than usual). Done this way, 4140 finishes nicely.

Right now, I am able to get a gorgeous finish at .0015" DOC, perfectly smooth, and almost mirror. I just want to be able to take lighter cuts because I am trying to get as close to .7500 as I can and its tough to get to .7530, then get a final pass that takes off exactly .003".