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I Just Bought A Rockwell 21-100 Milling Machine

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  • #16
    wdtom44,I have been toying with the idea of doing what you did to reduce the speed of mine. Would you mind posting some pictures of what you did? I follow your explanation but the details escape me. Thanks, Jim ( I probably rate a you suck also since I traded work for mine...)


    • #17
      Originally posted by jmm03 View Post
      wdtom44,I have been toying with the idea of doing what you did to reduce the speed of mine. Would you mind posting some pictures of what you did? I follow your explanation but the details escape me. Thanks, Jim ( I probably rate a you suck also since I traded work for mine...)
      Mine has the 110v motor, and I have been thinking about switching to a 220v three phase with a variable frequency drive to control motor/spindle speed.


      • #18

        I would post pictures but I haven't figured out how yet. But what I did was remove the stock motor base and make a 1/2" steel plate to fit in place of it. The plate is 7" front to back and 8" wide. From that I extended two 1 1/2" angle irons back to about even with the back of the round bar the head is mounted on. They were screw onto the bottom of the plate with the other angle facing up. From these angle irons I went up with four more short pieces to the height of the original motor base, then two more angle irons front to back to make the top of the new motor base. One angleiron, the left I think faces out to the left, the other faces in to the left and it came out just right for the motor to set on. Then I made a swing arm with ball bearings in the ends of the arms to fit the shaft that goes through the stock motor pulley which is mounted on the end of the swing arm about where it was when the motor was there. The motor goes towards the back and you can put what you want for a pulley on it. I tied the top angle irons together and put a support down from this frame, at the back, to the round rod the head mounts on. I hope this helps you. Tom
        Last edited by wdtom44; 05-10-2017, 10:11 AM.


        • #19

          The Rockwell 21-100 is a magnificent little mill, and you're going to LOVE it. For some jobs it's preferable to a Bridgeport. I personally needed something with a small footprint. I found lots of $2-$3k Bridgeport or Bridgeport knock off's. But I needed a small footprint and 110v would be REALLY nice since I don't need a ton of power, or table size & travel. I'm a gunsmith, mostly pistolsmithing, so I don't need a big mill at all. I just need something with good quality and like I said, small so it doesn't consume my entire garage.

          And for a hobby machinist who works out of his garage. The 110v option is really nice if what you need to do can be fulfilled with 110v, but these days 220v isn't hard to do at home. The little Rockwell is a quality machine that was used by the Navy who bought them by the truck load for the simple reason, it had a small footprint and even something as small as a submarine had room for a 21-100. In fact, all the manuals and documentation for the 21-100 are DOD publications...and they're a bit weak if you ask me. But fortunately it's a pretty darned simple mill so anyone can figure it out.

          I lucked out and found a Rockwell 21-100 made in 1961 that was sitting in the back of a Harley shop that hadn't been used in nearly a decade. Most are 220v but mine was a 110v which was perfect for me. The only flaw was one 1" are where someone milled into the table, but it's squarely under my mill vise so you never even see it. Other than that, the mill was in perfect condition. So I added a DRO from DroPro's, mounted a collet holder in the front just under the table, and a magnetic strip to hold all the wrenches that are used with this mill. I also bought little desk lamp, scrapped the base and fastened it to a Harbor Freight magnetic indicator base; work's perfect.

          Here's my baby.

          The other common US made "small" knee mill is the Clausing 8520, a good friend of mine picked one of those up and it's a fantastic little mill, maybe even a little nicer than my Rockwell

          So my mill has proven to be perfect for what I do which is pistolsmithing. I would take this mill over a Bridgeport every day of the week because it's so perfect for my needs. Bridgeport's are wonderful provided they haven't been beat to crap, and provided you have space to accommodate one.

          The little Rockwell has received the most sincere form of flattery in the form of being pretty much copied by the Chinese makers. Harbor Freight, Grizzly and I wanna say there was one other importer of what I refer to as the "Chinese Rockwell Knock-Off". And I've seen the Chinese Knock-Off's, they're damn nice little mills especially when you factor in the price. Had I not found my little Rockwell I would have bought the Harbor Freight one because it was cheaper both in cost and shipping; and they're all the same mill, so why pay more?

          Here's the Harbor Fright mill

          Here's the Grizzly

          Some further 21-100 information...

          US Navy Technical Manual TM 9-3417-211-14&p:
          Lathes US site (Rockwell 21-100):
          Rockwell milling lathes grinding brochure:


          • #20
            Congrats on new addition,looks at specs on UK site very well designed and sturdy for a mill that size.


            • #21
              Congratulations on the Rockwell 21-100, it's a wonderful machine for someone who has limited space.

              I got mine just over 3 years ago. I'm a gunsmith but I work out of my garage, so I have very limited space. I would have paid more for a smaller machine, as I found old Bridgeports and BP knock off's under 3k all the time. Found my 1961 Rockwell 21-100 in the back of a Harley shop, and it had been sitting there for about 10 years un-used. Only flaw was one small 1" spot where some idiot ran a bit into the table, but fortunately it's right where my vise sits, so I never even see it.

              I was all set to buy the Harbor Freight mill, which is basically a copy of the Bridgeport 21-100. Grizzly also sells a the same mill as HF, and one other company offers the same mill. I was going to buy the HF one because it was cheaper oth in price and shipping. And i have to say, those Taiwan small knee mills are very nice mills. But I found my Rockwell for $300.00 less than a new one from HF, so I thought; what the heck?

              Buying an older US machine I figured that parts would be much less of a problem than the new pacific rim machines. Add in the fact that the US Navy bought a bunch of these because they would fit on any ship and even a submarine. Well was I ever wrong on that one. Point of fact, that's probably the one real Achille's heel of the 21-100 is that parts availability is basically non-existent. Fortunately they were exceptionally well made and breakdowns are an exceedingly rare thing unless you really abuse them.

              Here's my machine. I added a DRO from DroPro's, and a semi-inexpensive import mill vise. Then I put a small collet holder on the front of the stand. The wheel from the table sticks out further so no worries of me bashing my shins on the collet holder. Next was a magnetic wrench holder to hold all the wrenches that I use for this mill; very handy. Last, I picked up a cheap desk light from Wal Mart, scrapped the base and hose clamped it to a Harbor Freight magnetic indicator holder. Very handy because I can move it to wherever I need it.

              Like I said, I'm a gunsmith and mostly pistolsmithing at that, so I don't need a lot of power, table space, or table travel; my needs are very easy and simple. Chances are I could have gotten away with a mill/drill but I really wanted a knee mill, and the 21-100 is like a machine custom designed for what I do; I couldn't have dreamed of anything better. I'm a little on the tall side (6'-2") so mine sits on 6"x6" boards that raises it up right close to where I need it (much easier on my back).

              So I paid $1,200.00 for mine which I thought was an absolute steal. Since then I typically find them in the 2k-2.5k price range, and 2.5k-3.5k with DRO's, so it seems I did rather did VERY well...actually you deserve a "YOU SUCK" comment

              Best of luck to you sir, I hope you enjoy a long and happy relationship with your Rockwell!

              The only manual ever made for the Rockwell 21-100 is the one put out by the US Navy, so in case you don't already have a copy...
              US Navy Manual:


              • #22
                Originally posted by tom_d View Post
                Mine has the 110v motor, and I have been thinking about switching to a 220v three phase with a variable frequency drive to control motor/spindle speed.
                Fortunately 110 has worked out perfectly for me, but I did once encounter a power limitation when I spun it up really fast to mill plastics; kept blowing the circuit breaker.
                If you want to stay 110v, the slick and cheap way to do so is to convert it over to a motor taken out of a treadmill. You can find free treadmill's on CL all the time. Those motors have a chit-ton of torque and they're infinitely adjustable for RPM; tough to beat for a replacement motor for machine equipment.

                For 99% of what I do, which is under 1,500rpm, the 110v works perfectly. But I think your plan for 220 will make you very happy, that will be really sweet!
                Last edited by DarkLord; 05-07-2017, 03:10 PM.


                • #23
                  I helped a friend get one at a auction a year ago. he paid $1,000 for it. I think he did well. I have a 8520 clausing.


                  • #24
                    Originally posted by bob308 View Post
                    I helped a friend get one at a auction a year ago. he paid $1,000 for it. I think he did well. I have a 8520 clausing.
                    A friend of mine has a Clausing 8520 which I personally think are just a little nicer than the Rockwell. He got his at an auction in the Bay Area, former shop class mill. Amazingly his 8520 is in miraculous condition, not even a mark on the table; wonder how it escaped abuse at a high school. Anyhow, you have a real gem in the 8520 Clausing; beautiful little mills.


                    • #25
                      The other 2 mills I have are on a heavy duty plastic pallet, with a 1/2" steel plate covering the pallet, the mill is bolted on, together forming a mill/steel/pallet sandwich, this make the mill very stable, raises it up about 6" and makes it easy to move the mill with a pallet jack if needed.

                      At this point I'm not sure if the mill will run on 240 vac single phase or if I'll go with a 3 phase motor and a VFD. We use (use, install, replace and sell) inverter VFDs at work everyday, if I can get one through work, I'll probably go that route.


                      • #26
                        I spent a good part of the day getting the Rockwell mill to the shop today. I went to the seller's facility and stripped the mill, down to the column and table/knee assembly. After lunch, where I bribed my friends, Trombone Pete and Norm, to pickup the stripped mill, on Norm's small utility trailer.

                        I based my purchase of the mill on my seeing the mill 2 years ago, last week, I saw it again, with a flashlight, it was far dirtier than I had remembered. Nothing serious, just grime and some swarf. With a few towels and some red Brakleen, the grime pretty much wiped right off.

                        The table moves smoothly side to side and back and forth, knee is tight and smooth, that table has some surface rust, but nothing serious. Over all, I very pleased so far.

                        I was unable to power up the head assembly, no 3 phase power (Not yet), but the spindle is smooth when moved by hand. Powering the head assembly is high on the To-Do List.



                        • #27
                          Please keep us informed of your progress, I'm always interested in what people do with their Rockwell's. Also, look into the Yahoo discussion group on the Rockwell mills.