PM-728VT working envelope capacity

[skcncx]

I'm in search of a few opinions and advice in my quest for the right sized bench top mill. Specifically related to the PM-728VT, at the top of my list. I say "right sized" because I know bigger and heavier is better but the plan is to do 95% milling in aluminum. No specific part/task, just to learn and have as another tool in my shop.

In general...

• What's a practical (approximate) capacity for the largest x/y/z part you could cut out, face mill, etc...?
  • Can the spindle w/end mill reach the entire surface of the 7" x 28" bed?
    
    
• Is the 16.25" Max Distance spindle a concern since you lose fair amount with drill chuck, mounted vise, drill bits/end mills extended?
  
  
  
• Can a fixture plate compensate (help minimize the bulk of a traditional vise) and also aid in "just as good" clamping setups compared to a vice?
  • I caught a thread discussing the tramming the 728vt of this mill and someone called out the https://saundersmachineworks.com/ fixture plate... they have low profile vice setups... though, in practice they may be more cumbersome than a traditional vice.... you can also mount a vice on top, though another 1" gone from vertical height.
  • I assume a 4" vise is the appropriate size for a 7" by 28" bed.
    
    
• Aside from trying to drill large holes 1/2" or larger in aluminum, is the 1 HP DC motor a good size for facing and general end milling with 1/4" to 1/2" end mills?
  • I know understand variable speed motors typically suffer torque at low speeds. I'm "guestimating" that won't be of concern in aluminum if sticking to smaller drilled holes and end mills.
  • Can a 1/4" end mill take a 1/4" DOC in aluminum for a slot?
  • Can a 1/4" end mill take off 1/8" of material on 1" thick stock on the end?
  • ... just trying to get a sense of what it can do without pushing it to it's limits.

Like my recent PM-1236T lathe purchase, I'm trying to get a "sense" of the real work the PM-728VT can handle.... not it's theoretical limits. As compared, the PM-833TV would be an option, but I'd rather not spend the extra $1,000 nor deal with the extra weight and bulk of the machine (though, that is better for rigidity).

The quill travel and max Distance spindle maybe important upgrades I may wish I had. Aside that, seems like the working envelope is similar.

 

[addertooth]

Adding goodies, such as a power feed (with safety stops) and a Digital Read Out may reduce total usable travel.

 

[maticulus]

I purchased a 728 last year as a beginner with a lot of ideas that I realized I really need a lathe for a good bit of which machinist wisdom says should be the first purchase, so I'm waiting on that and the mill has been idling for a while.

What I have found in my inexperienced use so far:
Usable table (spindle over) X=~ 20" and that's with a little of the saddle mount surface showing at the end and increased stress on the gib if the load increase on turning the hand wheel is any indication with a 4" vise in place. Y= full 7" plus an inch or more beyond the table both sides.

I have a 3" 5 blade R8 facer. 3" is the limit from what I recall reading, but I'm stepping down to a 2" and possibly a little less than that. The 3" facer can get choppy depending on the depth of cut and I've had to run it a bit faster than what rules suggest for a 5 blade in order to smooth it out. If the tram is not spot on it's definitely going to show in the finish. I'm new at this so it's possible with more familiarity with the nature of the cutter it might change my mind.

I had an incident while shaving an "L" shaped 3/8" steel bracket where I got too close to the angle. I believe I did stall the motor but hit the switch before the breaker tripped. The motor is strong, that little snafu knocked the tram out by a good bit and it took a few drill bit wobbling; drives for me to figure out something was wrong to check and correct it.

I drilled a 3/4" hole with a 3/4" bit 4" deep in a piece of aluminum without a problem.

I had to pickup the "T" slot kit from Little Machine Shop since PM didn't have it in stock. It's a pretty capable resource, however I'm spoiled by the 4" vice; PM HOMGE Ultra (I call it homeboy). While making an exhaust flange out of 3/8", 4x11" mild steel, I felt a 5" vice would have been better. I tried to face the plate in the vice, but the ends with the support I could muster were still too loose to avoid plate flutter and I didn't want to move the vice so I didn't start any trouble on cylinder head side of the plate, since it wasn't necessary.

The vice came with a base it could be rotated on, which I removed. Since the mounts on the vice are slotted, I'll need to figure out a way to key it to the table slots, as a flat bar underneath bends in the middle and distorts the tram when the ends are tightened to the vise as a result of the vise mounts being slotted, so the ends of the bar bend upward and center bows downward.

I've not had to think too much about the spindle over table space since I work close to the vise and that depends on what tool holders you're working with. I like the ER40 collet system and used a 1" rougher to carve slot like ports in the exhaust flange. I am glad I sourced my own DRO and scales. I opted for 1 thin linear scale through Aliexpress along with a 5 axis Ditron LCD and was able to mount the scale for the X axis on the front of the table in order to maintain full back side travel, except for what the vise takes up.

I have not done anything to wish for more power to date.

 

[7milesup]

If you plan on adding this or that to the 728, wouldn't you be better off just going with the 833TV? I had an 833T (the 833TV was not available then), and it was a rather capable machine. If I were you (@skcncx ) I would give the 833TV some serious consideration. It's only money, and you can't take it with you. Your welcome

 

[skcncx]

Adding goodies, such as a power feed (with safety stops) and a Digital Read Out may reduce total usable travel.

Yea, I've read that.... not sure about power feeds yet, but seems like at least one is what many do. DRO for sure. Though comment below, sounds like if you get creative and can find small scales, you may not lose any travel due to DRO scales.

I have not done anything to wish for more power to date.

Good to know!

I am glad I sourced my own DRO and scales. I opted for 1 thin linear scale through Aliexpress along with a 5 axis Ditron LCD and was able to mount the scale for the X axis on the front of the table in order to maintain full back side travel, except for what the vise takes up.

I plan to add an Aikron A30 dro, their small scales are slim. No more than 10mm thick by 15mm wide. That's what I ordered for my lathe.

I realized I really need a lathe for a good bit of which machinist wisdom says should be the first purchase, so I'm waiting on that and the mill has been idling for a while.

Logically, to the uninitiated, a mill seems more useful, but my lathe (after having my Atlas 618) got used more than I thought... now I'm waiting for my PM-1236T to arrive. My mill accessories to start will be bare.. since I've easily spent around $1,000 on just an Aloris tool post, BXA holders (PM brand) and several insert holders from latheinserts.com... I'm feeling the cost of trying to source much of it at one time.

 

[skcncx]

If you plan on adding this or that to the 728, wouldn't you be better off just going with the 833TV?

Well, I'm am considering it (loosely at the moment), kind of like I was loosely considering the PM-1236T over their PM-1228 which I was set out to buy... now I'm all in on the PM-1236T.... so it's not like I'm adverse to stepping up.... I'm just stubborn and (over) analyze and will try to really nail down the 1 or 2 reason it's worth stepping up to the larger 833TV for my use.

So... why would I be better off with the 833TV? I don't doubt it's better, but looking at the over all dimensions, it's not like it's much bigger... so that's not a reason. Certainly not if the capacity of the 728VT is enough for my use. 833TV has more mass and might be reason enough. 2HP instead of 1HP.

With no experience, it's really tough to gauge what the "right size" machine is.

A thought, and this is a similar thought I had as to why I went for the PM-1236T over the 1228 was that I figured I would be spending a fair amount on tooling and logically it makes sense to invest in tooling more so when you have a better machine to put it in use with.... a better foundation per say.

 

[7milesup]

"Bigger" is the correct size.
Trust me, I have been there. I started with a Harbor Freight mini-mill I bought from a friend for $300. He hadn't even used it. I had that about a year or so and realized it was just not even close to being big enough. Then I bought the 833T, which was such a huge, but excellent jump in size, rigidity, power, and overall usability. It was a decision I did not regret. But, alas, I sold that this summer and purchased a 3000+lb Sharp monster of a knee mill. Yeah, it's great!

Also, I should point out that I built my own stand for the 833T out of heavy-duty tubing, which was a magnitude above the factory stand in functionality.

 

[maticulus]

"Bigger" is the correct size.

Got it, bigger mill, new wife, because the current one isn't having it right now.
I had to put the cash equivalent in her hands to put in savings and finance the incoming lathe in order to con her into letting me get it.
The way things are going in the world, it was either get it now, or pay an awful lot more for it later.

 

[skcncx]

"Bigger" is the correct size.
Trust me, I have been there. I started with a Harbor Freight mini-mill I bought from a friend for $300. He hadn't even used it. I had that about a year or so and realized it was just not even close to being big enough. Then I bought the 833T, which was such a huge, but excellent jump in size, rigidity, power, and overall usability. It was a decision I did not regret. But, alas, I sold that this summer and purchased a 3000+lb Sharp monster of a knee mill. Yeah, it's great!

Also, I should point out that I built my own stand for the 833T out of heavy-duty tubing, which was a magnitude above the factory stand in functionality.

I'll take that to heart (my pocket book). A custom stand for sure. I'm working on my stand for my lathe at the moment.. will post pics when I have something to show.

Since the table is marginally bigger, sounds like "bigger" is more about the mass and rigidity the 833TV brings over the 728VT... while the 833 does have more quill travel and max z axis height.

 

[skcncx]

The way things are going in the world, it was either get it now, or pay an awful lot more for it later.

Isn't that the truth. I'm being sold/buying on fear... not a good position. Hence why I'm might be pushing my mill purchase sooner, figure it would be one day... but since I'll be making the road trip to PM for my lathe in Oct/Nov, might as well have them throw on a mill and save another round trip.