PRT vs PRS

[tradition_wood]

What are the, if any major differences between the PRT Alpha and PRS Alpha machines

[mriehm]

I've been wondering this myself. Most used SB's for sale are "T's", and I can only find info on the current "S's" on the website. I'm trying to decide whether it is worth buying a used "T" or if I should buy new.
Can anyone lead us to info. on comparing the two lines of machines?
thanks, Mike

[GlenP]

I bought a new PRS Standard. I compared buying a used PRT and it didn't make much sense to me. The cost of a new machine with the new faster, smoother 4G drives and all the lastest software is the way to go in my opinion unless you find a heck of a deal. Even then you should think about the cost of upgrades to make it cut smoother. For me on a PRT standard to a new PRS standard I was only looking at a few thousand dollars. ANd now you get vcarve and 3d software from vectric with new machines as a bonus. Just my 2 CND$ cents.

[richards]

Geoff,
I have a PRT-Alpha and my good friend just five miles away has a new PRS-Alpha. He got in a bind fulfilling a large order and asked me to do some cutting for him. I told him that I would, but that I would have him approve the first cut before accepting the entire job. Well, the first cut matched his sample. He approved the first cut and I got to spend some time just watching my machine do it's thing.

That being, said, I have added 3:1 belt drives (gearboxes) to my PRT-Alpha. Those belt drives have eliminated the 'chatter' that most PRT-Alpha owners have complained about.

If you are considering buying a used PRT-Alpha, factor in the cost of upgrading to the newer 7.2:1 Oriental Motor Alpha drives. Shopbot is offering that upgrade at a very reasonable price - and it elminates the 'chatter' problem.

Although I really like the design of the PRS-Alpha, the cut quality and the cut speed between my friend's PRS-Alpha and my PRT-Alpha were exactly the same. Because his PRS-Alpha has hardened rails, chances are that his machine will continue to cut well long after I have to replace my softer rails. (I can only hope that I have enough work to wear out the rails on my machine. If that day ever comes, my PRT-Alpha will have earned its keep many times over!)

By the way, I have another friend who lives just fifteen miles the other way, who has a pre-gecko PRT standard machine. Except for cutting at about 1/2 the speed of my Alpha, his machine cuts as good as, or even better, than my PRT-Alpha. If he upgraded his machine with the 4G kit, his speed would increase and his quality would be even better than it is now.

My recommendation is to buy a new machine if you can, but if the price is a little steep, or if the lead time is too great, don't be afraid of buying a well maintained used machine. At the end of the day, any Shopbot will have earned its keep.

[jeffreymcgrew]

I'll second what Mike says. The most obvious difference between the PRT and the PRS lines is that the PRS line has a much more robust construction in general.

There are several things we'd done to modify our PRT to solve some of these issues that are already solved with the PRS.

One thing that was mentioned was the rails. The PRT uses angle iron rails, which are bolted down to the verticals of your table. We've found after running our PRT for a year that adding a reinforcing steel piece (our table is wood) under the rail has helped somewhat, and are going to upgrade to a steel table when we move. Leveling and squaring these rails takes a while and isn't the easiest thing to do.

The PRS, to contrast, uses a large aluminum extrusion for it's base for the rails. This is much harder, straighter, and more stable than the PRT. So it's already stronger, I bet it's easier to square up and level, and they will last a long time and be stiff no matter what kind of table they are bolted to.

Another such thing is the Z axis. The PRT's z-axis can flex some, it simply held by bolts, and unless you get a special one it's only got about 6" of travel. We're going to reinforce ours with a plate of aluminum, as well as make more of a 'brace' frame for it so that we can square it up easier and keep it square longer.

the PRS, again, has a much more robust Z-axis, that looks easier to square up, and that's stiffer, and that has much less flex and more range of travel.

So while the motors and controller between the more modern and upgraded PRT's and the PRS are the same, there are differences that are there that I feel are worth it if you're planning on using your machine for heavy production use.

We bought the cheapest machine we could to get started, a PRT96 with used motors (special deal) and then since have gotten the 4G upgrade and done several things to get the table stiffer, and still aren't as good as the new PRS. I feel like we made the right decision for us, for we'd never done any CNC stuff before at all, but today if I could I'd buy a PRS instead if I was doing it all over again. Many of the issues we had to learn the hard way I think wouldn't have been so severe if we'd had a PRS...

[tradition_wood]

Well I am looking at David's "New in a box" PRT Alpha, I'll look into the upgrades, but for the price he is asking it sure seems like the way to go.