Can you tell me what (other than a minor initial cost difference) would make you choose a PM-833T over a PM-835S?
The first is a "precision" gear-head bench mill and the latter a very large knee mill. The difference in initial cost is $600. A 3-phase motor will probably cost you well north of $400 and Matt did tell me that it will be possible to get the 835S fitted with a 3-phase motor in future when I bought mine 2 years ago. At that time I was trying to make the decision you are making and am so glad I chose the knee mill.
All of the (expensive) add-ons you will need cost about the same except that you may wish to purchase a power feed for the knee, but that is strictly optional. I have a 6" Kurt vise (don't consider any alternative), the 3-axis DRO and every add-on you can imagine, all of which more than doubled the original basic cost.
I did buy a 3-phase replacement motor for my 835S ($500) but it is 3HP rather than 2HP so the cost may be slightly different. It is a direct replacement for the single phase belt drive unit and very easy to fit.
Yes there are belts to change in the 835S rather than gears in the 833T but I think that silence is golden. Besides the 835S is a true Bridgeport clone with a head that can nod when required (for real precision set up), it is very rigid, has a very high precision spindle (all Taiwanese), it has a large height advantage which I have found very useful when drilling large holes or using a tapping head, and with a VFD can do a great deal on one belt especially when combined with back gear. Since I got my VFD I have not had to move the belt for a very wide range of jobs. Its top speed with a VFD is much higher than the 833T At the low end with back gear, the available torque is huge). The 833T does not appear to have a proper power feed with auto stop for drilling and boring (I do not consider the Z-Axis power feed an equivalent feature).
Certainly it takes up a LOT of space and is very tall. With 5" of quill travel the fitting of a power draw bar is challenging (but possible).
I would be interested in how you come to your final decision.
This is a very good question and it made me give another "structured look" at my thought process. Here we go...
First I am hobby user, I like to produce high quality work but generally speaking I am not driving income from this tool. My rule is not to buy cheap because often times you will have to buy again. The mill will be used a good portion of the time as a "super capable drill press" so ease of use in this configuration is important. I drill on variety of materials from stainless steel down to wood with drill size as small as 0.6 mm to 6" hole saw. I am using a similar style drill/mill (Rong Fu RF-25 sold by Enco) for 35 years so I know very well what works and what does not work.
The ease of spindle speed change led me initially to the PM-833TV, but I figured out after I placed the order for a fully loaded 833TV that I need to rethink it. I am going with PM-833T with a plan to use a 3 phase motor and a VFD. I found a drop in 3 phase 2 HP motor that should do the job for slightly more than $250 including shipping from England. So hopefully this portion will work well and I will not hate the noise from the gearbox...
Table working height is very important to me, I am tall (6'2") so the low height of the table on the 835 and even lower when drilling or milling large items is a negative for me. On the other hand being able to raise the head easily is important so with the motorized option on the 833 it looks perfect. My old RF-25 is very cumbersome when it comes to changing height.
Machine footprint is important to me as bigger machine means less space for other "toys" in the shop so even if floor space is about the same, the ability to put the 833 on a stand that in my shop is a Harbor Freight drawers case is a big plus. I don't think that I will be able to put the 833 directly on the drawers as I did with the RF-25 but I can weld a cage that will allow me that functionality. See below a picture of my current RF-25.
The PM-932 and PM-940 look as a great alternative especially with hardened ways and the motorized Z axis but I was led to believe that the Taiwanese machines are better and they also come with 5 year warranty which might be a reflection of the quality or it is just a marketing gimmick (pay me more and I will give you a longer warranty...) who knows.
Last item is that the 835 or 935 looked a bit "too much" or "too complicated" to me. If I bought an RF-45 35 years ago (it probably was not available) I will not have to buy a new machine or I might decide that I need something better, who knows...
I hope I answered your question.
Ariel