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Mill / Drill improvements

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  • Mill / Drill improvements

    I have a Grizzly mill/drill. One of the heavier ones. Works probably as well as can be expected. With 20 or 30 pounds force, I can move the spindle about .003 total. Everything that can be tightened seems tight. The bearings are reasonably tight. I get the same deflection at the quill end or on something mounted in the spindle. Ways are fairly tight. Got it adjusted for about .005 backlash in the screws.

    This is enough slop to make most things look like they were chewed by small rodents. Has anybody managed to make any useful improvements to these things, like filling the column with lead or cement or such? It's never going to be a great machine, but maybe it can be a bit better.

  • #2
    5 thou is a lot better backlash than I had on my Mill/Drill, and I was able to get pretty decent surface finish.

    Are you calculating the correct speeds and feeds for the material?

    Are you locking the cross-gib while feeding (or vice-versa)?

    Locking the quill while feeding?
    "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."


    • #3
      Take lighter cuts.


      • #4
        use a rougher for all but light finishing cuts
        Ernie (VE7ERN)

        May the wind be always at your back


        • #5
          Originally posted by Chipslinger
          Take lighter cuts.
          Even with slow finishing cuts (.005) and a new endmill it's a bit rough. Everything is locked. Quill and other axis. It isn't too bad on surfaces with a fly cutter. Milling edges with the side of a 2-flute or 4-flute is a couple thousandths rough.


          • #6
            Bob, here is a link to the thread that Torker posted earlier this year.

            You mill drill guys....

            It deals with stiffening the column with a 3" steel shaft encased in concrete and allowances for tramming adjustments.
            I know he works the bajeezus out of that thing and he's very happy with the performance improvements.
            Home, down in the valley behind the Red Angus
            Bad Decisions Make Good Stories​

            Location: British Columbia


            • #7
              I had one of those evil little machines way back, chinese spindle bearings, a sloppy quill, and inconsistant table tightness, but with a little attention to detail it would give a nice finish. The big thing that it was very sensitive to was tool sharpness, and it liked HSS a lot better than carbide. One thing that I did was to add a power feed on the X axis and that really helped the finish. Even today, a power feed gives a much nicer finish than me cranking on the wheels.

              I would try going back to the basics - proper workholding, the right tool for the material, and speeds and feeds before you throw your hands up. There is a lot of really beautiful work done on crap machines, just takes a little more skill and patience.


              • #8
                Thanks. Cool. That's the kind of idea I was looking for. Looks like the base/column connection is the weak point in my setup. I doubt the column itself is flexing much but damping might help. I'll bet I can get some useful improvement by just replacing the column bolts. Maybe put a put a piece of inch and a half threaded rod in the column and put the whole base/column unit into compression. Easy to try before I mess things up and fill it with epoxy and such.


                • #9
                  Bob, if you can post the material, the cutter you're using, and the speed and feed you're running, it would give us a lot more insight into your problem.
                  "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."


                  • #10
                    This guy has done a LOT of tinkering/messing/finetuning his M/D and recorded and documented it really well .... check it out.

                    If everything seems to be going well, you have obviously overlooked something........


                    • #11
                      Rick Sparber's site is great. I have been following his shaper project for a couple of months and it is very enjoyable.


                      • #12
                        I have a Harbor Freight Mill Drill. It's their model 33686 that they've been seliing for years now. I bought mine around 1995. I agree, they could use more stability. I have read about filling the main tube with concrete but I can't somehow bring myself to do that.

                        One change that I did make, shortly after I got the machine had to do with the poor method that they used to index the R8 end-mill holders. I discovered that there was some looseness when the holders were inserted before tightening the draw bar. The holder would rotate a few degrees wither way.

                        After some thought, I completely disassembled the quill shaft unit and took a close look at it. I found that the manufacturers had simply drilled a hole in the quill and threaded it for a small metric socket head set screw. The end of the set screw would enter the notch in the R8 to hold it from turning. When I removed the set screw, I saw that it had gotten chewed away after about two weeks of use.

                        The repair was fairly simple. I looked in my motorcycle scrap box and found a loose roller bearing that was the same size as the indexing notch in the R8. I drilled the hole in the quill shaft to a few thousandths smaller then the roller and then, with an R8 holder inserted into the quill so that I could see the notch, I pressed the roller tightly into the hole until it bottomed out on the R8 holder.

                        The fit was extremely tight and to this day, I've not had any trouble with the repair at all.

                        One other rissue that I found was that the cast cover that goes over the worm used to lower the quill had a poor fit and it would rub on the shaft holding the three handles.

                        I used a boring head to clear the hole nice and round so that it was concentric with enough clearance to relieve the rubbing. Since it's only a cover, I was able to use the machine itself to make the repair.

                        I have found that the machine works better with HSS tools and small cuts. Obviously these machines have their limitations. At the present time I'm considering a used Bridgeport when I can find one nearby. I would still keep the HF unit, though. Besides having some use as a milling device, it's a really good drill press.

                        I left mine on 120 VAC because it runs just fine. I think it can be converted to 220 but the on-off switch doesn't seem that it would work. I'd have to change that and there's really no reason since the machine has ample power on 120.

                        That's my story and I'm stickin' to it.
                        Last edited by gnm109; 08-05-2008, 12:24 AM.


                        • #13
                          Pics please.

                          I'd appreciate it if the OP were to post pics (preferred) and/or links (alternative) so that I can see what type of mill-drill we are discussing.


                          • #14
                            Filling a tension resisting tube with an adhesive, setting, compression resisting compound is bound to make an improvement but it doesnt have to be heavy or wet. How about polyurethane foam might sound crazy but this type of of approach is used in aircraft and F1 to make very strong stiff structures. Even the building trade in the UK uses polystryene and polyurethane structurally in compression. Most house floors made of concrete are laid on polystyrene. High performance ally masts on yachts are foam filled to add strength
                            Try gluing two really thin sheets of ally (30guage) , even balsa wood with a sheet of polystyrene in between. You will be surprised how strong it is.


                            • #15
                              Climb milling?

                              This can happen with "climb milling" - if this is the case, try conventional/"up" milling.