Pm 728vt with stainless

[nighthawkFmobil]

For anyone with 728vt experience. I'm in the market for a mill and I'd like something smaller since my current shop is small. I'm all about experimenting with different metals. I'm into CAD so the possibility of cnc is very high within the first year. I think I'll throw a touch dro on it and have some fun with a manual mill for a while since I've never even touched one.

I could squeeze a smaller knee mill but we will see. I'm not getting the machine for anything super specific right now so I dont want to be limited in what i can cut(stainless). I know most people get these for aluminum and I plan to do a lot of aluminum. I run 304 on the pm1228 and I really enjoy it. I understand you're a bit limited by low end torque and and rigidity with these machines but I'm pleased with the results i can get with the 1228. Obviously hogging isnt a big deal to me. Would it be reasonable to expect good results with basic milling operations on the 728 in steel and SS as so long as I'm not working the machine and tools outside of their limits?

I plan on getting more mills eventually it just seems like its beneficial to have different machine for different types and sizes of work.

 

[Kiwi Canuck]

Hopefully David Best will drop by, he has quite a bit of experience with milling Stainless Steel and would probably have some feedback.

I like the look of the PM728VT and the PM833TV, both look like excellent choices when space and budget is limited.

The 833 is a much more robust machine and costs about $900 more so maybe worth a look at that machine if your budget can stretch a little.

You know it's our job to help you spend more of your money?

David.

 

[davidpbest]

If you're going to be milling 304, you probably already know from your lathe experience that there is a fairly narrow window of removal rate that produces good results. This is even more true on a mill. Too slow, and the material work-hardens and destroys your tooling pretty quickly. To fast and the heat generated cycles out of control in an instant and your end mill turns cherry red and the show is over. So you need torque. rigidity and consistent feeding. And you're going to be running the spindle below 1000 RPM with any end mill that is 1/4" diameter or larger. And you will have fewer problems overall if you climb cut with 304 which places a premium on gib adjustment, backlash reduction, overall rigidity. And something like a FogBuster (even with just compressed air and no coolant) to get the chips removed before they are re-cut will help tremendously.

For stainless, you definitely do not need the high RPM's offered by the variable speed mills like the 728TV or 833TV. If you can stand the increased noise of a geared head, you might be better off with that setup doing stainless IMO. Not that you can't mill 304 with the variable speed versions, but the extra torque of a geared head will have some benefit.

A power feeder on at least the X-axis will pay for itself within a year by keeping your feed rates steady leading to fewer destroyed carbide end mills. If you plan to add a DRO, it is really really helpful to have one that will tell you the feed rate. When I'm doing 304 on my 935, I'm constantly checking the inches/minute readout to keep the removal rate withing a certain band. Many budget DRO's do not have feed rate displays, which is one of the reasons I went with Newall DRO on my mill. If you plan to power tap 304, you will want high quality spiral point taps, and do not try power tapping with a spiral flute tap without a tapping head. See attached.

I don't have experience with the 727/728 class machine, but I did a lot of work with the original RF-45 from Rong Fu in 304. The 727M geared head is a a little light weigh at 450 pounds (without stand). My RF-45 was more like 750. So instead of the 728TV, I would encourage you to think in terms of the 932M, which at 850 pounds is certainly going to be a lot more rigid. If you can push the budget up to the 833T or 833TV, you're in a different league with a 900 pound Taiwanese-built machine, 5 year warranty, higher precision bearings, 5" quill travel, longer XY travels, and all that. The attached comparison of alternatives might bring a bit more clarity.

I would not attempt using a boring head on any kind of regular basis without power downfeed on the quill - for the same reason that consistent feed rates is really critical with 304. I know some users who are using the power feed head raise/lower on their 833 to bore, but have not heard about how it's worked out in more challenging materials like 304.

Keep in mind that I haven't actually run 304 on any of the above mentioned PM equipment, but my RF-45 could produce excellent results in 304 and 316 once the feed/speed formulas were worked out. In some respects the RF-45 produced better surface finishes than my PM935 because the square column and elimination of the Ram/Knuckle cantilever setup which contributes to higher rigidity. Whatever you get, plan to spend some time and destroy a few end mills working out the feed/speed formulas, and it will help if you can stick to a couple diameters of end mills you come to know rather than switching between 5 or 6 with different diameters, flute counts, etc. Hope this helps.

 

[nighthawkFmobil]

Hopefully David Best will drop by, he has quite a bit of experience with milling Stainless Steel and would probably have some feedback.

I like the look of the PM728VT and the PM833TV, both look like excellent choices when space and budget is limited.

The 833 is a much more robust machine and costs about $900 more so maybe worth a look at that machine if your budget can stretch a little.

You know it's our job to help you spend more of your money?

David.

Honestly I struggled posting this because I'm sure if I did deep enough I could find the answer but I searched for a whole and couldn't find anything about anyone's experience milling ss on a light 1hp

If you're going to be milling 304, you probably already know from your lathe experience that there is a fairly narrow window of removal rate that produces good results. This is even more true on a mill. Too slow, and the material work-hardens and destroys your tooling pretty quickly. To fast and the heat generated cycles out of control in an instant and your end mill turns cherry red and the show is over. So you need torque. rigidity and consistent feeding. And you're going to be running the spindle below 1000 RPM with any end mill that is 1/4" diameter or larger. And you will have fewer problems overall if you climb cut with 304 which places a premium on gib adjustment, backlash reduction, overall rigidity. And something like a FogBuster (even with just compressed air and no coolant) to get the chips removed before they are re-cut will help tremendously.

For stainless, you definitely do not need the high RPM's offered by the variable speed mills like the 728TV or 833TV. If you can stand the increased noise of a geared head, you might be better off with that setup doing stainless IMO. Not that you can't mill 304 with the variable speed versions, but the extra torque of a geared head will have some benefit.

A power feeder on at least the X-axis will pay for itself within a year by keeping your feed rates steady leading to fewer destroyed carbide end mills. If you plan to add a DRO, it is really really helpful to have one that will tell you the feed rate. When I'm doing 304 on my 935, I'm constantly checking the inches/minute readout to keep the removal rate withing a certain band. Many budget DRO's do not have feed rate displays, which is one of the reasons I went with Newall DRO on my mill. If you plan to power tap 304, you will want high quality spiral point taps, and do not try power tapping with a spiral flute tap without a tapping head. See attached.

I don't have experience with the 727/728 class machine, but I did a lot of work with the original RF-45 from Rong Fu in 304. The 727M geared head is a a little light weigh at 450 pounds (without stand). My RF-45 was more like 750. So instead of the 728TV, I would encourage you to think in terms of the 932M, which at 850 pounds is certainly going to be a lot more rigid. If you can push the budget up to the 833T or 833TV, you're in a different league with a 900 pound Taiwanese-built machine, 5 year warranty, higher precision bearings, 5" quill travel, longer XY travels, and all that. The attached comparison of alternatives might bring a bit more clarity.

I would not attempt using a boring head on any kind of regular basis without power downfeed on the quill - for the same reason that consistent feed rates is really critical with 304. I know some users who are using the power feed head raise/lower on their 833 to bore, but have not heard about how it's worked out in more challenging materials like 304.

Keep in mind that I haven't actually run 304 on any of the above mentioned PM equipment, but my RF-45 could produce excellent results in 304 and 316 once the feed/speed formulas were worked out. In some respects the RF-45 produced better surface finishes than my PM935 because the square column and elimination of the Ram/Knuckle cantilever setup which contributes to higher rigidity. Whatever you get, plan to spend some time and destroy a few end mills working out the feed/speed formulas, and it will help if you can stick to a couple diameters of end mills you come to know rather than switching between 5 or 6 with different diameters, flute counts, etc. Hope this helps.

That information is gold to me.

 

[nighthawkFmobil]

Hopefully David Best will drop by, he has quite a bit of experience with milling Stainless Steel and would probably have some feedback.

I like the look of the PM728VT and the PM833TV, both look like excellent choices when space and budget is limited.

The 833 is a much more robust machine and costs about $900 more so maybe worth a look at that machine if your budget can stretch a little.

You know it's our job to help you spend more of your money?

David.

I was embarrassed to make the post because I couldn't really find the info on my own. I'd be glad to have yall help me spend my money haha

 

[davidpbest]

Honestly I struggled posting this because I'm sure if I did deep enough I could find the answer but I searched for a whole and couldn't find anything about anyone's experience milling ss on a light 1hp


That information is gold to me.

I’m glad it was helpful. Let us know what mill you decide to buy.