# Am I expecting too much from my pm940?



## FE427TP (Nov 3, 2019)

I bought a low hours used pm940 a while ago as my first mill. I am trying to use a shars carbide insert end mill and fresh inserts.  I've locked the non moving axis' and the quill. the tool says 3000 rpm and a very aggressive cut something like 30ipm I don't remember the exact specs off the top of my head. I was trying high speed and building up feed of cut but I am getting a lot of vibration before I get anywhere near the recommendation. I have no cooling if that matters .4 depth on the z axis and .1 on the y axis in 1018 cold rolled bar stock. And maybe 2 ipm across the x axis but the machine is vibrating enough to move a wrench and my calipers across the table. Am I expecting too much of this machine to be able to handle a cut like this? I'm not talking the 30 ipm just the vibration. I went with the carbide because of some hard material I had to work on that ate up my 3/4" hss end milk that didn't justify eating. Seeing the machine vibrating has me nervous to turn up the rate of feed. Chips are small but coming off darker.


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## darkzero (Nov 3, 2019)

Yes, don't expect your machine to perform like a rigid CNC machine. You didn't mention what size your indexable endmill is & how many flutes but say for smaller than 3/4" or 1" I prefer traditional endmills. I bet a traditional carbide endmill may give you better results. If you need to take that heavy of a DOC try lowering the spindle RPM or switch to a roughing endmill or a smaller endmill. 

Those recommended speeds & feeds don't always work with smaller hobby sized machines. I don't have a PM940, I have a PM45, the only time I take a DOC that deep are with 3/8" or 1/4" endmills. Play with speeds & feeds even if it's way off what the tool is recommended at, you should be able to figure out what your machine is happy with using that tool.


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## FE427TP (Nov 3, 2019)

Good point. I hadn't mentioned the size. Shars part number 404-1862, 3/4", 3 flute. Page 103 on the catalog. I'm just using a generic insert and I think I'm having other issues from the cheap inserts as the cuts aren't plumb. I was taking a total of 1-1/8" vertically off of the bar stock in three passes and approximately .1 from each side to take 3/4x1.5" to half inch thick. I was just making a bar the same width as a half inch bolt to press a u shaped channel in some sheet metal. I can feel the ridge between passes and it's really visible with a straight edge. They appear seated properly. Do you have any recommendations for an economical carbide 3/4" end mill? Seems like the prices escalate rapidly with size


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## jaek (Nov 3, 2019)

I think with your axial and racial depths of cut and the insertable end mill you only have an insert in the cut a quarter of the time. Which explains the vibration.

A conventional end mill with helical flutes will vibrate much less.


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## darkzero (Nov 3, 2019)

Unfortunately I don't have any recommendations on brands or a specific end mill for 3/4" carbide. I just buy whatever is name brand (mostly USA) & a good deal on ebay. Surprisingly Chinese carbide is actually pretty good unlike HSS where you can get absolute crap. They say this is because the need "diamond" to make/grind the carbide endmills as opposed to HSS where they can just use the cheapest rock they can find.

Your indexable endmill may just be fine for the job, try slowing it down, 3000 rpm is way too fast. Also try some better inserts. Those generic C2 C5 uncoated inserts are nice & cheap but usually don't perform well.

Or try a roughing endmill if you want to hog material away quick. Coarse tooth for faster removal & heavy cuts, fine tooth for harder materials.


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## jwmay (Nov 3, 2019)

So you’re trying to take a .400” depth of cut in hardened material? I don’t have much advice for you sadly. I’d be splitting that DOC into eighths. Then again, I’ve read carbide needs to get in deep. But if what you’re doing ain’t working, you may want to start by easing up on the numbers. You could have it done with more lighter passes long before your newer, better, USA made carbide endmill arrived in the mailbox. Apologies if I misunderstood the issue. 

Plunge milling is a pretty quick route to success when needing to take significant depths of cut also. That may be an option I guess.


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## ttabbal (Nov 3, 2019)

0.400... Wow.. I don't run that on my Bridgeport. Mostly because I'm chicken.


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## mksj (Nov 3, 2019)

The DOC seems reasonable for a 3/4" end mill, but the feed rate seems a bit extreme (due to the high RPM). The RPM is way higher than I would use. Similar to what WIll is suggesting I would try carbide or powdered metal/cobalt end mills. I routinely remove that amount of material in steel with a 3/4: end mill, typically around 6-8 IPM with a full size bench knee mill, Can't remember the RPM, but something in the 800 RPM range. Using a feed and speed calculator using a 3Fl 3/4" carbide at 800 RPM with a SFM of around 300-350 and a chip load of 0.0045 I get a feed rate of around 9-11 IPM. Cobalt would be a bit less SFM.   I do not follow the 3000 RPM.  If the machine was more rigid, you could increase the RPM and the IPM would increase for the chip load, but in your case I doubt it is taking much of a cut out of the steel, just deflecting..

As far as 3/4" end mills, I typically use the 3/4" Minicutt 3 flute wave cut (930 series) or 4 flute powdered metal end mills. They are less expensive and do well in a wide range of materials. The 930 and some of the other end mills use a wave profile which is a semi-rougher but gives a smooth surface.
Carbide I often can pick up Widia/Hanita, SGS, etc. really whatever I can find at a decent price. I then check out the specs and coating as to the application. Some examples below.









						3/4" Cobalt End Mill 3/4" Shank, 4-Fl, 1-1/4" LOC Minicut International M42  | eBay
					

Minicut International 3/4" Cobalt End Mill with 1-1/2" Length of Cut, 3-1/2" Overall Length. ID# minicut 3/4" M-42 9/20.



					www.ebay.com
				











						M35110 3/4 x 1 1/2 4FL Widia™ Series CG-4R Corner Radius Endmill 2737172  | eBay
					

Helix Angle 30°. Right-hand spiral, right-hand cut. Corner Radius 0.020". Type Finishing Corner Radius End Mill. Series CG-4R corner radius. Corner radius for applications that require it. Center cutting.



					www.ebay.com
				











						Widia / Hanita 620V19077, 3/4" x 3/4" x 1 5/8" x 3 7/8" Wavcut Roughing End Mill  | eBay
					

P/N 620V19077. Corner Chamfer Angle - 45 degree. Finish / Coating - Uncoated. of Flutes - 4 - Centercutting. Made in USA. Flute Length - 1 5/8".



					www.ebay.com
				











						1 NEW FALCON / SGS 3/4" DIAMETER CARBIDE END MILL. 4 FLUTE. 4" OAL USA MADE M201  | eBay
					

4" OVERALL LENGTH. 1-1/2" LENGTH OF CUT. FALCON TOOL WAS SUPPLIED WITH ALL SGS END MILLS. We describe our tooling as it is, we do not hide anything. CENTER CUT. MFG 100% MADE IN USA.



					www.ebay.com


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## FE427TP (Nov 3, 2019)

jaek said:


> *snip*
> A conventional end mill with helical flutes will vibrate much less.



that provides a very understandable explanation I hadn’t thought of. Thank you.



darkzero said:


> *snip*.
> 
> Your indexable endmill may just be fine for the job, try slowing it down, 3000 rpm is way too fast. Also try some better inserts. Those generic C2 C5 uncoated inserts are nice & cheap but usually don't perform well.
> 
> Or try a roughing endmill if you want to hog material away quick. Coarse tooth for faster removal & heavy cuts, fine tooth for harder materials.



Thank you, i’ll try to find some better ones to try out




mksj said:


> The DOC seems reasonable for a 3/4" end mill, but the feed rate seems a bit extreme (due to the high RPM). The RPM is way higher than I would use. Similar to what WIll is suggesting I would try carbide or powdered metal/cobalt end mills. I routinely remove that amount of material in steel with a 3/4: end mill, typically around 6-8 IPM with a full size bench knee mill, Can't remember the RPM, but something in the 800 RPM range. Using a feed and speed calculator using a 3Fl 3/4" carbide at 800 RPM with a SFM of around 300-350 and a chip load of 0.0045 I get a feed rate of around 9-11 IPM. Cobalt would be a bit less SFM.   I do not follow the 3000 RPM.  If the machine was more rigid, you could increase the RPM and the IPM would increase for the chip load, but in your case I doubt it is taking much of a cut out of the steel, just deflecting..
> 
> As far as 3/4" end mills, I typically use the 3/4" Minicutt 3 flute wave cut (930 series) or 4 flute powdered metal end mills. They are less expensive and do well in a wide range of materials. The 930 and some of the other end mills use a wave profile which is a semi-rougher but gives a smooth surface.
> Carbide I often can pick up Widia/Hanita, SGS, etc. really whatever I can find at a decent price. I then check out the specs and coating as to the application. Some examples below.
> *snip*]



 I wasn’t pushing it that hard with the vibration I was getting. My machine will do around 2000rpm in high gear. I’ll try to attach the end mill spec sheet with suggested feed and speed, I’m below the bottom end for Speed&Feed.


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## mksj (Nov 4, 2019)

The speeds and feeds are for an industrial machine and not a hobby machine. If you check online calculators you will get lower SFM/RPM numbers. I worked with another individual about 2 years ago that was milling a lot of steel finger for a sheet metal brake and was having a lot of chatter/burning up inserts, and this was with a 3500 lb mill. I recommended that he lower the RPM and the inserts lasted much longer with a lot less vibration.  I believe it was a Shar's 2.5" cutter head similar to the one you are using, but larger. A 3/4" indexable end mill I would be pushing the RPM up, but in steel probably not higher than 1200 RPM.   So my suggestion is more based on previous experience with larger 90 degree indexable end/shell mills, but then it is machine/material specific. Also the quality of the insert and the amount of material being removed. I gave him some of my Iscar APKT inserts which worked better. I also think the vertical Z axis cut you are taking is at the limit of the size insert, which is at 0.4" or slightly under. SFM for the Iscar inserts in steel is 260-660 SFM. I usually can achieve 1/2 the rated SFM on my knee. I can take the type of cuts you are describing with a 3/4" end mill with no problem, but with an indexable end/shell mill I take wider shallower cuts. My Z axis DOC is usually up to 0.1", so maybe try wider and shallower. Use a rougher for rapid material removal.

This what what I told him at the time and it worked better (reducing the RPM), he was initially running at around 700 RPM at 10 IPM with a 0.02" DOC  in CR flat bar steel.   "My inserts for steel have a SFM at around 250, which for a 2.5" shell mill I get an RPM of 400. On the shell mill, with a 0.004 in/tooth feed rate at 400-500 RPM and 5 inserts I come up with a feed rate of something in the 8-10 IPM. The DOC of 0.020 is close to what I use per pass sometimes I do a bit more, usually  based on chip color and machine vibration. When using carbide inserts on a manual mill I usually shoot for the lower end or down to 50% of the insert rated parameters. In steel, I would try 400 RPM at 8-10 IPM, you may be going a bit too fast on the RPM for steel. I use the same heavy cutting oil lubricant you use, but for steel maybe something with a higher sulfur content may work better. I often see Anchorlube G-771 Metalworking Lubricant or Mobilmet 766 Cutting Oil recommended, but you have more experience than I do on this. I do not see flood coolant normally for machining steel with a manual mill, I would do as you are doing and brush it on."


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## phazertwo (Nov 4, 2019)

I have a 940CNC and there is no way I would attempt that cut.

As it was stated above, the numbers you're pulling from the spec sheet are starting point numbers for industrial machines that probably weigh in excess of 10k lbs (if not MUCH more).  No way you are going to touch those numbers with a standard knee mill, much less a hobby bench top.  .4" DOC x .1" WOC x 30IPM = 1.2^3 MRR.  That'd be a lot in aluminum for your machine, much less hardened steel.

That being said I have cut .25" DOC and .05" WOC very reliably in steel using a 3/8" carbide 4 flute endmill.  Finish pass was 0.75" DOC at .010" WOC.  Parts came out looking amazing.

PZ


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## shooter123456 (Nov 5, 2019)

I have a similar end mill that I use on my PM-25.  That one really does not like a large DOC.  I know that in theory, you should be able to cut as deep as the insert goes, but I have similar vibration issues anytime I go above maybe .2" DOC.  I usually run that one around .1" DOC and increase the WOC.  Traditional end mill do much better for me if I want to take a larger DOC.


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## macardoso (Nov 5, 2019)

I also I have a Shars APKT indexable endmill (3/8" single flute flavor) and have found it to be too rough on my G0704. It worked OK on the very large knee mills I had at school, but I have given up using it on a benchtop. One issue is that the inserts aren't very sharp. This is OK on big machines with a lot of spare HP, especially since it helps with tool life, but really creates a LOT of cutting forces. If you want to machine aluminum, consider trying the APGX insert. It should fir your same tool but has a razor sharp ground edge for non-ferrous metals.

But to echo what was said above, use a corncob roughing endmill for bulk material removal and some good carbide solid endmills for everything else.


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