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Spindle recommendations for a lathe toolpost grinder?

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  • Spindle recommendations for a lathe toolpost grinder?


    I want to add a toolpost grinder to my lathe. Eventually I would like to CNC it for making things like involutes and cycloids, or one-off cutting tools.

    My lathe is just a little 7x14. Preferably I would like to have the motor located remotely, via flexible shaft or pneumatic. It would make positioning of the compound slide easier.

    Problem is, I don't have a clue about different manufacturers of grinder spindles, what they are good or not good for, and was hoping for some advice. Any wheel attached to it would probably get no bigger than 50-75mm/2-3". I realise that to work with tiny grinding bits, it will also need to operate at very high RPM


  • #2
    those little air die grinders are pretty popular or mounting a dremel/ flex shaft is another option. Didn't think a whole lot of my dremel tool poster grinding experience (lots of chatter and bounce) but it's better than nothing in a pinch.

    Other than that a small ER11 or ER16 powered spindle from China is your best bet for a complete unit. They sell them for CNC routers.


    • #3
      Was the dremel the source of the chatter? I've only owned one dremel tool (dremel stylus), and haven't had a great experience. I had to return it, because the on/off button failed after about a week or two. It was nicely aligned, spun at max speed with no significant vibration. However, the replacement unit vibrated horribly at nearly any speed. I sent it back again, they sent me another one just as bad. Again, I sent it back, but this time insisted that Bosch technicians inspect the tool before shipping it to me. I finally got a better one, but it still vibrated at the highest speed settings. I gave up trying again.

      It now belongs to my mum who uses it for model ship building. She doesn't use the high speeds so it isn't an issue.
      Last edited by Swarfer; 12-18-2016, 10:47 PM.


      • #4
        I actually have a black and Decker version which is a step up from a Dremel in that it has a small ball bearing spring the spindle. I don't know if the chatter was from the tool or the crappy undressed wheel I had on it. When I need it again I'll definitely see the wheel on the grinder and see if that helps.


        • #5
          I used a 56,000 RPM pencil grinder on my lathe a few times for grinding work and it never worked well. The spindle actually gave out during a job, it got all wobbly in the housing. I think the ball bearings partially exploded.

          You can often find Dumore spindles on eBay. I'd go for those if I was looking to buy a toolpost grinder spindle.


          • #6
            For a small lathe, the Foredom line of flex shaft grinders can be had in 1/3 Hp and variable speed to 15,000 rpm. The hand pieces are ball bearing equipped with collet shaft holders ( up to 1/4"). It would be fairly simple to construct a mount for your tool post.



            • #7
              I do like matts idea of using a cnc spindle unit, seems sensible, good bearings etc, I've had no luck with dremels, Wizards (b&d) or air, poor finish, better than nothing but only just, TP grinders are only made of platinum with solid gold wires over here, judging by the price so I think I'll try a spindle unit
              Don't laugh I had better finish using the hub of a bycycle wheel once, not a bad spindle as it turned out


              • #8
                Looking at the motorized spindles on Ebay the issue I see with them is that they only go up to about 12K RPM. Now that'll be fine for 3/4 and larger diameter stones. But it's not enough for smaller sizes to really make them work well. But I see that there are also higher powered water cooled motors that run up to a max speed of 60K RPM. That should do the trick and allow the use of smaller grinding points.

                The other thing I see is that these motorized spindles are not all that small at roughly 2 inch diameter by around 5 to 6 inches long. That's going to fill up the room on a 7x14 pretty quickly. LIkely need to pull off the tail stock. Or if you want to grind an item held between centers it may turn out that you need an odd off set mount for the unit.
                Chilliwack BC, Canada


                • #9
                  Hmm, yeah, I haven't really thought much about the space available on the lathe bed. My tailstock is way too high anyway, about 0.3mm, so I have to shim the head before I can use it.

                  I looked at those water cooled motorised spindles, but yeah, they are fat. A spindle housing (without incorporated motor) that large would hold an enormous stone

                  boslab, how fast were you running the bicycle spindle? The fastest cyclist on record is only doing around 1200 RPM

                  RWO, those Foredom ones look pretty nice. Though a max RPM of 12000 is about 15.7m/s (3100 SFPM) surface speed on a one inch wheel

                  Andre, yeah, a pencil style seems just a little light duty No Dumore in my region though

                  What would be some other way the home shop (CNC) machinist could grind a cycloidal gear surface?


                  • #10
                    Hiya Swarfer, I built one with a used ebay Sherline milling spindle and an ebay 24vdc scooter motor. It's mostly completed but I need to finish a few coolant details here: and here for details on what I'm doing for coolant management, post #28

                    I'm using a 4" CBN wheel which keeps the speed well within the Sherline's 10K rpm limit. Personally I think it will go faster but not by much. I plan to use 1" alum oxide points as well right at the 10K limit. Probably not fast enough but we'll see how it goes. HTH

                    "Accuracy is the sum total of your compensating mistakes."

                    "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton


                    • #11
                      Gotta watch the speed rating of some of those points.



                      • #12
                        boslab, how fast were you running the bicycle spindle? The fastest cyclist on record is only doing around 1200 RPM
                        I'm going to guess about 6000, pedalling furiously, I stuck a pully on one end to an old elecric motor, 1500 rpm, then a smaller pully on the other end, can't remember sizes as the thing was a tinkering exercise with plastic pulleys.


                        • #13
                          I have some older Dremel units that always seem to work decently as far as finish. I used them to grind chuck jaws to be straight again,and they did OK. If I really want good, I have a TP grinder, but I hate using any grinder on the lathes.
                          CNC machines only go through the motions


                          • #14
                            I have made an adapter to mount my Unimat head stock on my SB9 quick change tool post. It is sized to hold the Unimat at center height with the usual fine adjustment via the tool holder. The Unimat spindle is not perfect, but worlds better than any Dremel or other hand held tool.

                            I was doing some drilling with it in that photo, but I can mount large abrasive wheels directly on the spindle and small abrasive points in a collet.

                            I can also mount it directly on the compound with a different adapter and the Unimat column for a greater range of positions.

                            And I will save you the trouble of calling me out: yes, I was milling with a drill chuck and not a very good one at that. All I can say is that it worked. I have since made a collet adapter and have a set of ERs for it.
                            Last edited by Paul Alciatore; 12-20-2016, 03:55 AM.
                            Paul A.
                            SE Texas

                            And if you look REAL close at an analog signal,
                            You will find that it has discrete steps.


                            • #15
                              I have made my first toolpost grinder more than 10 years ago based on a Rotorzip tool. The spindle speed is 30000 RPM and it has a 1/4" collet. Put 1" grinding stone in it and it cuts steel like a butter. To put it on a lathe I have made an adaptor, which clamps on the Rotorzip nose and gets installed in place of a regular tool. Rotorzip is much more robust tool than Dremel and can easily use a 1" stone.

                              Recently I have bought a Habor Freight die grinder with extended nose, which is even better candidate for a toolpost grinder. It has 25000 RPM no load speed and also has a 1/4" collet. For bigger wheels the speed can be reduced by reducing the power supply voltage (you will loose power as well). I like this design because the grinder spindle is separate from its motor and rides in 2 ball bearings. I have a long term project in my mind to replace the bearings with high accuracy angular contact ball bearings, put a proper preload on them and install labyrinth seals. This will essentually create a real grinding spindle, capable of machining with good accuracy and surface finish. The tool will install on the lathe via an adaptor, similar to Rotorzip one.