PM-728VT working envelope capacity

[7milesup]

Got it, bigger mill, new wife,

No, jeepers! That would be very expensive. I just keep mine around so I can buy more tools. (just kidding)

 

[jwmelvin]

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.

Yes, mass and z- capabilities. When my pm-30mv showed up, I thought “It’s cute.” It’s been good but I have a Bridgeport clone now and only rarely use the -30mv. I got lucky with the clone and paid a lot less for it than the PM mill. At least with mill tooling, a lot of it works across an upgrade (so long as you stick to R8 spindles). Larger vise and some other things but the smaller tooling still works too.

 

[Aaron_W]

I have a Clausing 8520 which is in the same general class as the PM 728. Other than being a knee mill it has roughly the same power, and work envelope. I've been very happy with my mill, however if you are even thinking bigger might be the way to go, then you may be right.

The Y axis on the 833 is almost 33% greater 11" vs 8-1/2" which is pretty significant. There is also the additional 4" table to spindle so 25% more (16" vs 20"), the Y and Z are the two areas that smaller mills tend to be most challenged and you can see how much more the 833 gives you there.


The extra 1-1/4" of table width could be the difference between comfortably fitting a 6" vise or not, but I'd check with others before counting that as an advantage. It may still be too small to recommend a 6" vise. I know even a 5" vise is pushing the limits on my 6x24" table, a 4" being much more suitable. It seems like most with PM 7"x mills tend to favor 4" vises as well. If the 833 can take a 6" vise that is a definite advantage in its favor, and it could certainly take a 5".

Beside the added work holding size, there are loads more 6" vises available than 4" or 5" because of the proliferation of Bridgeports so the odds of finding a decent used Kurt are much higher. There is also little cost difference between a 4" and 6" vise buying new, again because of the volume difference. A Kurt DX4 retail is $728, a Kurt DX6 retail is $779, only $51 more.

The 833 could also probably better take an 8" rotary table, where again 6" is generally preferred for the smaller mills.

I'd guess most of these smaller mills can manage a part 12-14" long, X axis (working area not total length) pretty easily but I'd think 6x6" in the X and Y is the upper limit of comfortable, the 833 would certainly expand the size capability by 2-3" in these dimensions.

Twice the weight is also not an insignificant factor, but unlike the dimensional stuff where it fits or doesn't, rigidity can at least be addressed to some extent by taking smaller cuts. Of course if it appears the 728 is plenty of mill for you, lighter and cheaper can certainly have their own advantages.


Think about the size of the projects you have planned and imagine setting them up within the travel distances of the 728, I'd use 5x7x15" to be conservative and leave some room for the occasional slightly larger project.

 

[skcncx]

@Aaron_W Thanks for your input, that's exactly what I'm looking for to give me a sense of what I'm buying.

I've been very happy with my mill, however if you are even thinking bigger might be the way to go, then you may be right.

I'm not really looking for bigger, but I'm also trying to avoid something that I'll be constrained with right away. It's always a toss up... I want the biggest and smallest machine that's of good quality.

The extra 1-1/4" of table width could be the difference between comfortably fitting a 6" vise or not, but I'd check with others before counting that as an advantage. It may still be too small to recommend a 6" vise. I know even a 5" vise is pushing the limits on my 6x24" table, a 4" being much more suitable. It seems like most with PM 7"x mills tend to favor 4" vises as well. If the 833 can take a 6" vise that is a definite advantage in its favor, and it could certainly take a 5".

PM pairs the 728 with a 4" and the 833 with a 4" or 5"... so my guess is that those are right size given the machine. I wasn't sure how much a fixture plate can do and it seems they are super useful. Seems similar in concept to my welding table with 5/8" holes on 2" centers... it's great with all the accessories and tooling to make setups easy.

I'd guess most of these smaller mills can manage a part 12-14" long, X axis (working area not total length) pretty easily but I'd think 6x6" in the X and Y is the upper limit of comfortable, the 833 would certainly expand the size capability by 2-3" in these dimensions.

Twice the weight is also not an insignificant factor, but unlike the dimensional stuff where it fits or doesn't, rigidity can at least be addressed to some extent by taking smaller cuts. Of course if it appears the 728 is plenty of mill for you, lighter and cheaper can certainly have their own advantages.


Think about the size of the projects you have planned and imagine setting them up within the travel distances of the 728, I'd use 5x7x15" to be conservative and leave some room for the occasional slightly larger project.

The 5" x 7" x 15" capacity is super helpful.

No particular project, which does complicate it, I just know aluminum is probably all I'll every put in it so the fact you've had no power issues with your Clausing 8520 is a good reference. I know I can always take lighter passes on a smaller machine but I feel at some point that's true if I got my file out and machined that way. Does the 833 with 1 extra HP and double the weight/rigidity really double what the 728 can do... maybe, hard to tell, so many factors I assume to make a blanket statement.

Certainly have something to think about. If both are in stock when I pick up my lathe in Oct/Nov it may be a last second decision.

 

[Dabbler]

but looking at the over all dimensions, it's not like it's much bigger

The larger X,Y,Z travels make the 833 more useful. Everything you do, to adding work holding, to cutter diameter reduces your work envelope.

but here is a kicker:The spindle to column dimension matters. I had a really nice small mill, with envelope of 22 in X 12 in Y and 24 in Z. However the short fixed distance between the column and the spindle meant I had to cut off the handles on my tap wrench to tap holes - and bunch of other niggling things that just bothered me. So I sold that mill and bought a BP clone in the 9X49" size.

Every time you have to 'change up' a machine tool it costs a lot of money. Not just the sales price versus the buy price. Also tooling changes, and there's moving stuff out and moving the new one in. So the buy once and cry once thing has been real for me, just in reverse. I went from a 12X37 lathe to a 14X40 lathe to a 15X60 lathe. So I have a little experience in the matter.

Now most of my projects are in a bit larger size normal, but even steam engine guys have to get creative with their machines to make their bigger parts. Have a look at Blondihacks series on Youtube and see how creative she had to be to get this project done... (in my shop that is a very small sized project)

Everyone is different and one has to stay in budget. But if you can afford the 2" greater work envelope in X,Y and Z, you will never regret it.

 

[7milesup]

Just as an FYI I would not put a 6" vise on an 833TV mill. I had a 5" on mine, and I felt that it was a very nice size for it. Now that I have a large knee mill, I also have a 6" Kurt vise. I have a hard time imagining that 6" on my 833. There are a few threads on here where someone has asked about vise sizes on an 833.

 

[Aaron_W]

@Aaron_W

No particular project, which does complicate it, I just know aluminum is probably all I'll every put in it so the fact you've had no power issues with your Clausing 8520 is a good reference. I know I can always take lighter passes on a smaller machine but I feel at some point that's true if I got my file out and machined that way. Does the 833 with 1 extra HP and double the weight/rigidity really double what the 728 can do... maybe, hard to tell, so many factors I assume to make a blanket statement.

Certainly have something to think about. If both are in stock when I pick up my lathe in Oct/Nov it may be a last second decision.

I've worked with Steel on my Clausing and it will easily take bigger bites than I'm comfortable taking. My mill is heavier (about 600lbs), but a little smaller and only 3/4hp motor, 3p with VFD control. I'd imagine the 728 would have no trouble at all with aluminum and would be just fine if you had a project using steel. Biggest consideration for me would simply be the size. I moved to my current mill from a Sherline mill, so a huge step up in performance, although I will mention even my Sherline could work with steel, just smaller bites.

I'd say the biggest drawback to my mill is the MT2 spindle. Not a huge issue, but it does limit some of my tooling options. The 728 has an R8 which is super common, so tooling won't be an issue.

I started off making model parts, and still mostly do little stuff but I'd still love to have a Bridgeport sized mill just for the room to grow. No room for anything bigger than the Clausing in my basement though. My wife is quite accommodating but she gave a hard no on having the head of a mill stick up through the kitchen floor.

Just as an FYI I would not put a 6" vise on an 833TV mill. I had a 5" on mine, and I felt that it was a very nice size for it. Now that I have a large knee mill, I also have a 6" Kurt vise. I have a hard time imagining that 6" on my 833. There are a few threads on here where someone has asked about vise sizes on an 833.

I was wondering about that. Wasn't sure if it might be just big enough, but you confirm that it isn't, so one less advantage. No choice now but for him to look at one of the 9x machines.

 

[skcncx]

but here is a kicker:The spindle to column dimension matters

I didn't even think about that. The 728 indicates 8.75" and the 833TV shows 11.75". That does seem like a pretty big advantage.

Every time you have to 'change up' a machine tool it costs a lot of money. Not just the sales price versus the buy price. Also tooling changes, and there's moving stuff out and moving the new one in.

I hear ya... I'm tooling up from scratch for my PM-1236T and well, I'm feeling the expense. Just a good set of basics, I'm already over $1K. That's just an Aloris QCTP (20% off) and several tool holder from latheinserts.com (BTW, great experience working w/Curtis) and some miscellaneous stuff.. still need to order several more of PM's BXA tool holders.

I'll likely start bare bones on the mill.

But if you can afford the 2" greater work envelope in X,Y and Z, you will never regret it.

Yea, I'm starting to look with a bit more intension at the 833TV.

I'd say the biggest drawback to my mill is the MT2 spindle. Not a huge issue, but it does limit some of my tooling options. The 728 has an R8 which is super common, so tooling won't be an issue.

Yea, seems like the R8 on both the 728 and 833 is a great setup.

 

[jwmelvin]

When I looked at a machine collection for sale, I passed on the Clausing 8520 because it wasn't significantly larger than my pm-30mv. It certainly would have been a big upgrade for work within the smaller envelope, but I knew I wanted both more rigidity and a larger working envelope. Other people have different requirements (or just weight them differently). The -30mv's belt drive played a significant role in choosing that machine over one that was larger but had a gear drive. I'm not sure that was the right tradeoff, now that I know how much rigidity and mass matter at times. The -833tv is a significant step up, in my view; the price reflects that.

 

[Aaron_W]

When I looked at a machine collection for sale, I passed on the Clausing 8520 because it wasn't significantly larger than my pm-30mv. It certainly would have been a big upgrade for work within the smaller envelope, but I knew I wanted both more rigidity and a larger working envelope. Other people have different requirements (or just weight them differently). The -30mv's belt drive played a significant role in choosing that machine over one that was larger but had a gear drive. I'm not sure that was the right tradeoff, now that I know how much rigidity and mass matter at times. The -833tv is a significant step up, in my view; the price reflects that.

I am very happy with my 8520, but I wouldn't have made that change either. A lot of work to trade out and you give up a fair bit of size / capacity to gain the knee. The 8520 is a great small mill, but ultimately it is a small mill.