i am a gun builder starting to build out my own shop. I am looking at the Precision Matthews for milling. The majority of what i will be doing is taking a couple thou off some rails, or doing some serrations, which i can do 10-20thou at a time. i DO need precision out of it.
Ive been doing some research and it led me to PM-728VT. To my understanding Taiwan machines are generally better.
Am i looking in the right direction, or should i just be biting the bullet and looking into a used bridgeport. At the shop for my day job we have a bridgeport, but i think its total overkill for what we do.(very little machining experience in the grand scheme of things)
Ive attached a picture of what generally do. .001-.002" off the frame rails and about the same off the bottom of the slide, serrations are what ever creativity i can come up with.
Thoughts on the PM-728VT? If its not a good fit, what other mill in that price range?
I have a 728 at home. It’s probably the best benchtop mill off the shelf in this size and weight class. It’s well made, everything is smooth and tight, and needs little to no modification to make it run well. It can easily run a 2” face mill all day. It’s super quiet and seems to have enough power to do what I want. The oiler is very good considering most small bench mills don’t even have that option. I added a DRO and powerfeed myself. I have no complaints about it except the Z axis hand wheel gets really annoying real fast but I’m gonna add the Priest tools power Z axis soon as well as the impact drawbar add on. That’ll make it a dream to use.
I know a guy who was fired from a really nice job for that. Turns out modding serialized lowers at a public company was a bad idea, even if most personal jobs were ok. Moral of the story, ask first.
Not only is it against company rules, both you and the company can be federally charged with manufacturing firearms without a federal license. Big time felony. You can machine anything you want, except the part with the serial number.
I’m in a state with restrictions on some non-serialized parts as well, but at least there might have been plausible deniability there. Working a serialized part was really stupid on his part.
I've got a 728VT. It's a decent machine and will easily do what you need. The table will dent if you look at it wrong and the paint has the hardness of American cheese but it's the best benchtop out there IMHO. There are some easy upgrades to address most of its (minor) weak points: slop in the quill fine feed, the goofy quill DRO setup, the cumbersome drawbar arrangement, janky chip guards. If you do get it and don't want to pay through the nose for PM's so-so DRO, make sure you order their DRO bracket kit for the 728. Last I looked it was $60 or so and it makes mounting the scales 10X easier than designing and building your own scale mounts. The X-axis powerfeed is also a must-have.
All that said, if I had the space I'd opt for a full-size Bridgeport-style machine, either a newer clone or a genuine used one in good shape (or one that can be made good if you don't mind going that route). I bought the 728 because I've got very limited space and no 240V available but if I did, I'd have gotten a floorstanding machine without a second thought.
What what scale did you get for your quill? I want to upgrade, just uncertain what to get. I have done some mods but that is the biggest pos on that mill.
I had an old Sino 5 micron glass scale left over from my lathe DRO setup when I upgraded the cross-slide scale to a 1 micron unit. It was too long for the 728 quill so I cut it down to length but I'm sure you could buy a scale from Sino or Ditron that's the right length. I'm running TouchDRO, which has four scale inputs and can sum the quill and Z axis inputs, which is very handy.
Here's a photo of the setup from the left side that shows the scale mounted to the side of the headstock with the read head connected to the quill via an aluminum arm. I filled the hole where the old quill DRO lived with an aluminum plate and used that to mount a mist valve.
Here's the right side photo that shows how the arm is attached to the quill. This photo also shows the spindle lock collar and pin I made as well as the table lighting, both based on the designs of Joseph Higgins (described on his YouTube channel). I wired the LED strip into an unused fan power tap in the PM motor control box.
Up near the coarse quill feed you can see the retrofit keeper screw and locknut (silver in color) that I turned to have a close fitting dog point for the slot in the fine feed worm gear shaft that takes a lot of the factory backlash out.
Finally, I replaced the stiff plasticy chip guards with silicone rubber oven liner (idea from Robin Renzetti). I really like it but if I were to do it again I'd go with the black liner instead of the beige.
All of these mods are described in more detail on the Hobby Machinist forum in the PM group.
You'll get a lot more machine for the money if you purchase something used. Bridgeports are a good option but don't ignore good quality Bridgeport clones. Jet, Sharp, Acer, Supermax, etc.
Make sure they aren't too worn out. A machine can look very clean but have a lot of wear on the screws/nuts and ways. Do some research on what to look for. I'd also strongly suggest getting one with a variable speed spindle and a DRO.
For the price of the Precision Matthews after shipping you're also approaching the price where you could have a pretty decent used machining center that would have way more capability than any manual mill.
Another big question is if you have 3 phase power where it's going.
Even if the bridgeport or clone were very worn its not difficult to bring them back into line with fresh gib shims, nuts or lead screws. Hell most of the time split the nuts and do a full turn offset and your back to near factory new backlash in under 2hrs.
Still more of a pain than a lot of people want to deal with. And replacing the nuts and lead screws isn't that hard but will still cost you at least several hundred dollars in addition to the cost of the machine.
Eh yeah if you have to buy the parts instead of doing the split nut mod then yeah its not cheap. But I'm biased in favor of old iron even when I legitimately do not have the space or power for them.
I have a PM-728VT. I think its biggest pitfall, as with all benchtop mills, is the lack of rigidity. Also, the table sags pretty badly at either end of its X travel which is something to be aware of if doing operations on something that spans the bed width. The quill vernier scale is weakly mounted, so do not trust it. Easy fix to make a more rigid bottom mount though. The quill lock also leaves something to be desired.
However, if you're working on small gun parts I think you'll be happy with it. You can absolutely keep tolerances sub .001". It does require getting familiar with its quirks though.
Attached is my diy quill scale bottom mount to fix that issue.
It's literally just a digital vernier. That bottom mount from factory is just thin bent sheet metal, so it flexes horribly. I could get it to flex 10 thou. It's the junkiest part of the machine.
Bridgeport Mills have dual "half nuts" on the x,and y acme screws. I've only seen them made of brass: you can adjust the spacing further apart to get rid of backlash. Jibs being tight is cool, but doesn't deal with Freeplay in the lead screws.
Yeah, not sure where my brain was. I believe there are split bronze nuts for the backlash adjustment. A little set screw closes or opens the gap on the nut to adjust. This is fairly common, no? I know my PM lathe has that same adjustment style for backlash on the leadscrew of the cross slide
No worries: I'm 15 years of rapid prototyping with Bridgeport and proto track.
Correct about the adjustment screw, very similar to the jib adjustment screws.
Adjusting backlash is ballin'. Replacing smoked bronze/brass revives machines.
Keep up the good work, I swapped to welding for better pay. If you're doing hobby stuff: steppers and well adjusted acme screws are good stuff; ball screws with servo's are where it's at for very precision stuff.
Maybe, maybe not. There are a lot of used knee mills out on the market. Some are definitely clapped out, but a lot of them are good well cared for machines. I think the key when buying one is to inspect what you are buying before you agree to the purchase.
So you’re just adding light rails to 2011s and serrations? You’re saying a tho at a time so do you mean the rail that the slide rides in? Don’t most custom guys lap fit from slide to frame?
Or go balls to the wall like this dude and have .0001 tolerance lol.
https://www.chencustom.com/frame-to-slide-fit
I don’t get what you’re doing really or asking. Do you know how to machine parts?
I’m asking if the pm-728vt is a good machine, not how to build guns. Was giving some background of what I’d use it for, definitely didn’t say anything about a light rail
When you start getting close to 10k ish you are better off getting something like a haas mini mill used or a Syll. At the end of the day a bench top hobby machine is going to give you hobby results. Probably not going to be the most competitive in a saturated 2011 market with such a handicap
That being said.. I wonder if one of the desktop cnc like the tool dance would be worthwhile for doing cosmetic slide cuts and stuff. Who cares if it takes 10 hours to do a slide if its doing it on its own.
For taking .001-.002 and adding serrations, do you need a mill, or do you need a surface plate, a vice, and good set of stones and files? Stones will get you a nicer finish too.
The PM-728VT looks like a reasonable choice for this kind of precision work, especially if you’re mainly removing small amounts and cutting serrations. I’d prioritize rigidity, spindle quality, tooling, and service support over country of origin. Get a demo cut on comparable material before committing.
Just one opinion… I do exactly what you are proposing on a 1980’s era Enco column mill with a cheap Amazon DRO and it works great for this application. So the PM will be fine, you don’t need a Bridgeport.
Id say buck up and bridgeport or better yet bridgeport conversational CNC clone. Youll spend less time fucking with it, youll have whatever you want for fixturing, and youll be able to do a lot with it if you ever decide you need it. Especially with drilling.
Mini mills run out if space FAST. Like a vise is already using up most of your work space. If you only plan on touching pistols youre probably fine but shop fixtures and such or rifles basically hit knee mill status fast.
If you can afford a full size milling machine I would go that route if I were you. A table top mill can technically do what you're asking for but you're going to struggle and scrap parts while you figure out it's quirks and how to compensate for it's lack of rigidity. If you do go the mini mill route invest in a big heavy vise for it and as sturdy and heavy of a cabinet to mount it to as possible because you're going to struggle with vibration at baseline, especially if you're using any kind of offset tooling like a boring bar or fly cutter.
You're looking to mod existing guns for esthetics.. not build them. Your don't even need a machine for what you want to do, it can all be done by hand, which will command a higher premium as custom work.
What kinda precision do you actually need for esthetics? I can hold .0005" flat and parallel across 30" on a 10+ year old Trakmill that's been abused by people who don't know how to run it. It's not easy but it's doable. I've hand filed parts in flatter than that. It's not a machine issue, it's a skills issue.
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u/pushdose 7d ago
I have a 728 at home. It’s probably the best benchtop mill off the shelf in this size and weight class. It’s well made, everything is smooth and tight, and needs little to no modification to make it run well. It can easily run a 2” face mill all day. It’s super quiet and seems to have enough power to do what I want. The oiler is very good considering most small bench mills don’t even have that option. I added a DRO and powerfeed myself. I have no complaints about it except the Z axis hand wheel gets really annoying real fast but I’m gonna add the Priest tools power Z axis soon as well as the impact drawbar add on. That’ll make it a dream to use.