Capabilities: Is a 1 hp PM mill enough for 18-8 stainless steel? Or 2 hp?

[Gladiataar]

IMO, you absolutely want the TV head. I don't really think you're going to be particularly torque limited, and if you find yourself torque limited, you can limit your DOC (probably only an issue with the 304).

50 RPM is plenty low enough, but there is no such thing as too much speed! 1500rpm out of the T head is too little. For HSS tooling, there IS no 'minimum' RPM, though carbide there is. However, smaller endmills/drills are TERRIBLE to use without sufficient RPM. The problem ends up being that what breaks an endmill/drill tends to be 'feeding faster than the cutter is able to cut material in front of it'. With bigger mills, you can feel this happening, however running something like 1/8" mill, or a #40+ drill without a ton of RPM means you're going to not feel it, and just snap it right off.

I have a 1/8" cutter that if I run at 1500 RPM will snap if I feed it any faster than a crawl. At 2200 RPM (max of my millrite), takes only a moment of feeding too quickly to cut off. At 3000 RPM on my new mill will cut all day as fast as I dare to feed it.

If you're doing a lot of aluminum, speed is going to be key to nice surface finishes. Get the 3200 RPM head! The lesser torque is going to be sad, but the only time you're cutting at sub-~400 RPM (particularly on Aluminum!) is with a big cutter: at which point you'll want a fly cutter anyway on a machine this size.

Got it! TV head on the PM-833 it is! Several others responded with the same recommendation, so that's the way I'll definitely go. Thanks for the detailed scenario on your reply here. Knowing exactly how a small diameter cutter behaves at certain rpms gives me some real life examples of what I can and can't do -- or at least shouldn't risk doing. @ErichKeane mentioned something about not going below 229 rpm with a 1/2" end mill in 304SS either, so I guess I just won't be going as low as I thought I'd be.

 

[ErichKeane]

Got it! TV head on the PM-833 it is! Several others responded with the same recommendation, so that's the way I'll definitely go. Thanks for the detailed scenario on your reply here. Knowing exactly how a small diameter cutter behaves at certain rpms gives me some real life examples of what I can and can't do -- or at least shouldn't risk doing. @ErichKeane mentioned something about not going below 229 rpm with a 1/2" end mill in 304SS either, so I guess I just won't be going as low as I thought I'd be.

Note that is the 'speed to cut it at' according to the app, which seems to be a fairly conservative RPM, not the 'minimum'. BUT, I found that anything less than ~75% of that number (well, the numbers this app gives) in carbide tends to leave some cruddy finishes. HSS seems to not care about the speed being too low.

 

[B2]

Hi David,

Thanks. Always good to get your advise.

It seems my PM HAV-6 vise does this, one just needs two to make the trampoline geometry. I am sure the Kurt vises are great, but I am pretty happy with what PM (Matt) sold me in 2017. On the other hand, lifting two ..... !!

Dave L.

 

[ErichKeane]

Hi David,

Thanks. Always good to get your advise.

It seems my PM HAV-6 vise does this, one just needs two to make the trampoline geometry. I am sure the Kurt vises are great, but I am pretty happy with what PM (Matt) sold me in 2017. On the other hand, lifting two ..... !!

Dave L.

Kurt vises shine in particular when you have two of them. There are a few import manufacturers that make pretty darn nice ones, and some imports that are garbage, its hard to tell since they are the same castings, but some companies (I presume PM!) put in the QA to make sure they are getting the good ones!

BUT Kurt shines when you need two vises to be the exact same height. For a while they would sell you a 'matched pair', but my understanding is most of their models are now so precisely ground, they believe that any two purchased identical models are a 'matched pair'!

 

[davidpbest]

XYZ mentioned something about not going below 229 rpm with a 1/2" end mill in 304SS either, so I guess I just won't be going as low as I thought I'd be.

Reason enough for you to get a Feed/Speed app for your smartphone. When cutting stainless steel, the most important consideration is to keep the tool cutting a chip of a thickness roughly equal to 0.001". The factors that contribute to that are the feed speed, the RPM of the cutter, and the diameter and number of flutes of the cutter. If you go too slow, stainless will turn into chewing gum and clog the cutter and leave a terrible surface finish. If you go too high in either feed or speed, heat increases with a similar result. Coolant can help, but most important is chip evacuation so that you aren't re-cutting the chip just removed. HSS has an SFM low enough that it's more difficult to find a sweet spot than using a carbide cutting tool. DM me if you want more background on this.

And since you'll be dealing with R8 tooling and the need to change tools, you might be considering a power drawbar. To that end, I offer the attached.

 

[Gladiataar]

You might want to consider sticking with 4-flute carbide end mills for your stainless work. I typically run a 1/2" 4-flute uncoated carbide end mill at 800 RPM which is right in the sweet spot of the 833TV, and at 0.100" DOC, 75 percent tool engagement, a feed rate of 6 IPM. If you are doing a lot of 304, you will want to get a good feeds & speeds calculator for your smartphone (I use FSWizard), and having a DRO that displays your feed rate is worth whatever extra it costs over one that doesn't display feed rate. Machining stainless is much less forgiving in terms of getting your feeds and speeds dialed in, and you will want some kind of chip evac system like a Fogbuster or similar MQL coolant system (see the attached PDF).

I feel like you guys are starting to give me inside trader information here. Seeing as I already own this end mill, knowing what specs to run it at in 304SS for the 833TV sweet spot is gold ... pure gold!

I do plan on acquiring 3-axis DRO, but as quite a few have mentioned here, it can be had for cheaper if I go aftermarket. Some have even suggested specific brands, which it great, I'll definitely be checking them out. BTW, for clarity, I should've given a breakdown of the $1100 DRO price that I earlier quoted: $699.99 for DRO hardware kit + $399 installation fee = ~$1100.

Thank you for the write-up on the available coolant systems as well. Surprisingly, I don't have an air compressor in my shop right now, so I may have to deal with manually applied coolant for a while. Also, I don't plan on making large volumes of parts with this mill. I was sort of hoping that I wouldn't need a fully automatic coolant system, at least not initially.

 

[davidpbest]

I do plan on acquiring 3-axis DRO, but as quite a few have mentioned here, it can be had for cheaper if I go aftermarket. Some have even suggested specific brands, which it great, I'll definitely be checking them out. BTW, for clarity, I should've given a breakdown of the $1100 DRO price that I earlier quoted: $699.99 for DRO hardware kit + $399 installation fee = ~$1100.

My strong recommendation is to take the $400 you'd spend on having the supplier do a quick-and-dirty installation of the DRO, and apply that money to a DRO with a feed speed inciation, and do your own installation using many of the online resources to guide you in the installation. DROPro's has a terrific set of "how to" videos on all the considerations. But there are tons of other resources. Don't be intimidated by the requirement to drill and tap an M4 or M5 hole in your mill. Practice on plastic or a scrap of aluminum first to get a feel for it. The attached may help.

 

[davidpbest]

Kurt vises shine in particular when you have two of them. There are a few import manufacturers that make pretty darn nice ones, and some imports that are garbage, its hard to tell since they are the same castings, but some companies (I presume PM!) put in the QA to make sure they are getting the good ones!

BUT Kurt shines when you need two vises to be the exact same height. For a while they would sell you a 'matched pair', but my understanding is most of their models are now so precisely ground, they believe that any two purchased identical models are a 'matched pair'!

I bought a Kurt 6" D688 in 2003, then added a Kurt DX6 in 2018. I found the Z-heights withing 0.0003". Two years later, I sold my D688 and got a second DX6 so that both vises has the same maximum opening capacity. The two DX6 units are indistinguishable from each other using a Mitutoyo tenths indicator in terms of reference surface dimensions.

Irrespective of which vise you buy, make sure it conforms to Kurt mounting hole standards, that way you can buy replacement or soft jaws at prices less than retail material costs from monsterjaws.com (no affiliation).

MonsterJaws Mfg - High Quality Chuck and Vise Jaws (Machinable Soft Jaws)

MonsterJaws Mfg Chuck Lathe Mill Vise Machinable Carvable Soft Jaws Aluminum Steel

monsterjaws.com

 

[Gladiataar]

Several of you said that: 1) The lack of a power down feed on the quill, 2) Lack of a power y-axis option on the PM833, are not absolute dealbreakers for the type and volume of parts I'll be making. As a newbie, I have all intention of going slow and sticking with manual feeds initially anyway, but it's good to know that there are quite a few experienced machinists/hobbyists out there who've done without, or at the very least, say that you can get by without. For what it's worth, I was going to try using the z-lift motor in a sort of experimental powered boring operation, should the need arise.

The other point several replied on was my concern with the vise and its orientation on the PM-833's "smaller" table. Perhaps my description wasn't clear. The way I see it, a 6" vise has 6" wide clamping jaws that open to (sometimes) over 9". I just assumed that the shape of the part -- and orientation of planned cut line-- would dictate how you would mount a vise on the X-Y table. Several of you even included pictures of their vise(s) mounted with their long axis perpendicular to the X-axis. However, what I also assumed was that, on occasion, a user would mount their vise with its long axis running parallel to the X-axis. Now, if the slots in the X-Y table were not far enough apart, as in the case with mill tables smaller than 9" in Y-direction, the mounting holes in the vise may be too far apart to line up with the slots in the table. Should this be the case with the PM-833, as I think it is, I wouldn't even have the option of mounting my vise "horizontally" (i.e. with the clamping screw running parallel to X-axis). I saw this as a mounting limitation -- and a mark against -- "smaller" bench mill tables. No such limitation exists when mounting a 6" vise on a knee mill's larger table. One obvious solution for bench mill owners would be to simply buy a smaller (narrower) 5" vise instead. Which is what I was planning on doing anyway, due to the unpleasantly hefty weight and awkward bulk of a 6" vise.

 

[davidpbest]

Several of you said that: 1) The lack of a power down feed on the quill, 2) Lack of a power y-axis option on the PM833, are not absolute dealbreakers for the type and volume of parts I'll be making. As a newbie, I have all intention of going slow and sticking with manual feeds initially anyway, but it's good to know that there are quite a few experienced machinists/hobbyists out there who've done without, or at the very least, say that you can get by without. For what it's worth, I was going to try using the z-lift motor in a sort of experimental powered boring operation, should the need arise.

The other point several replied on was my concern with the vise and its orientation on the PM-833's "smaller" table. Perhaps my description wasn't clear. The way I see it, a 6" vise has 6" wide clamping jaws that open to (sometimes) over 9". I just assumed that the shape of the part -- and orientation of planned cut line-- would dictate how you would mount a vise on the X-Y table. Several of you even included pictures of their vise(s) mounted with their long axis perpendicular to the X-axis. However, what I also assumed was that, on occasion, a user would mount their vise with its long axis running parallel to the X-axis. Now, if the slots in the X-Y table were not far enough apart, as in the case with mill tables smaller than 9" in Y-direction, the mounting holes in the vise may be too far apart to line up with the slots in the table. Should this be the case with the PM-833, as I think it is, I wouldn't even have the option of mounting my vise "horizontally" (i.e. with the clamping screw running parallel to X-axis). I saw this as a mounting limitation -- and a mark against -- "smaller" bench mill tables. No such limitation exists when mounting a 6" vise on a knee mill's larger table. One obvious solution for bench mill owners would be to simply buy a smaller (narrower) 5" vise instead. Which is what I was planning on doing anyway, due to the unpleasantly hefty weight and awkward bulk of a 6" vise.

You can always toe-clamp the vise to the XY table in whatever orientation you desire - you are not restricted to aligning the vise mounting-holes to the T-slots in the XY table. You can always employ toe-clamps to the base of the vise, or use a fixture plate to mount the vise or the material being machined. I recommend you explore the alternatives to a conventional vise for workholding if you are indeed planning to do production work. Fixture plates are one example, mod-vises are another, and vacuum pallet systems are another. Lots of ways to do workholding that don't involve conventional vise use.