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Sizing a Quick Change Tool Post for a Grizzly G9249

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  • Sizing a Quick Change Tool Post for a Grizzly G9249

    I am looking to put a QCTP on my lathe.

    I am on the wall as to piston or wedge. This still one of the reasons I have not pull the trigger. I like piston for the ease of recreating parts as they wear.

    The next is size... there is 100, 200, 250, 300 and AXA, BXA, CXA???

    The link below is what I have:

    What it will be used for... I am a home machinist. I don't do production, but I spend a lot of time in the shop.

    Played with the thought of make one but can not find a detail drawing and not knowing the size I need.

    The other big question I have is where do I get the measurement of the dovetail for each size? Are they standard? One series size works with all of them??
    Last edited by outlawspeeder; 11-20-2017, 11:42 AM.

  • #2
    no comment on size, athough you can do some top of compound to center line measuring that'll help - the different sizes work with different distances, rather than size of swing. You're probably on the line between AXA and BXA.

    go for wedge, doesn't cost much more and it's a bit more repeatable/ secure than piston.

    for each size (AXA, 250-100 etc) the dovetail dimensions are available and should be consistent. So you should be able to use holders from one make/ source on the tool post from another.


    • #3
      I think you will find that you want the AXA size. Some years back I tripped over what seemed like a good price on a piston style AXB size that was listed for being good for my 12x36. It works but it's actually a hair too big. Here is a link to download the Aloris CATALOG PAGE. On page 4 is what you want.

      The critical measurement is your height of the spindle centerline above the top of the compound rest. On the AXB size holders 1/2" square HSS fits without modifying the holder but on tools with even slightly raised tips such as a 1/2" square bodies for carbide inserts the QCTP holder actually ends up being too tall and I can't get the holder to sit low enough without fouling the compound. So the bottom of the holders needs to be milled away slightly. On the AXA size this shouldn't happen. But look up the drawings and figure this out for yourself.

      In my case the distance from the top of the compound to the spindle center is 1 3/16. Note that the AXB holder has a lower thickness of 5/8". So I really only have room maximum for a 9/16" tall cutter. And if it's a smidge more than that due to an insert then it won't fit.

      The other issue is that with it being a piston style holder I'm running all the tool holders down right at the bottom of the height range. So the piston is only bearing on the upper bit of the holder. I haven't pushed things hard enough for this to become a problem but it could since the lower half of the tool holders don't have any pressure to lock them. Like I mean about a quarter of the piston is peeking out over the holder.

      So all in all the size you want is an AXA size. Not only will this result in more flexibility with the tool holders but it'll put them up more in the center range of the post itself.

      What MAY happen is that you find that the 1/2" slots in the basic holders are snug and need to be relieved in the mill by a little bit if you want to use any metric sized shank tools or those with a rough finish which is actually just a hair over 1/2" square. But that won't take much. And at least the post itself will be the right height.

      As for piston vs wedge I am a huge believer in having contact and support as close to the cutting edge as I can get. So for my money the wedge style is better. The piston style pushes the tool holder away from the post and the only locking points are the angled faces in the dovetail and the piston face against the base of the dovetail cutout. The outer two surfaces do not make contact. The wedge style expands the dovetail on the post and draws the holder inwards so the outer two faces are locked in contact with the post as well as the dovetail angle faces. The only part not in contact is the base of the dovetail cutout. So piston is two surfaces and a piston contact area. Wedge style is four solid faces of contact. Wedge wins by a knockout.
      Chilliwack BC, Canada


      • #4
        To me an important feature of a quickchange toolpost is repeatability. Change from one tool to another and get the same size part. I tried a piston style and saw quickly that repeatability varied a lot and that was the end of it. I bought an Aloris post which repeats with near perfection.


        • #5
          [QUOTE=outlawspeeder;1144968]I am looking to put a QCTP on my lathe.

          I like piston for the ease of recreating parts as they wear. QUOTE]

          I don't get this comment since with a quality tool post and quality tool holders, everything is hardened and ground and will last a lifetime with no concern for wear. Aloris and Dorian offer top notch equipment. A cheaper alternative is Phase II. It is an Asian import, but well made. I have used their tool holders on my Dorian post for at least 15 years with satisfaction. I did replace the set screws on early ones with good quality screws from McMaster-Carr. No other changes needed since.



          • #6
            My understanding is we have the same lathe, mine is an 80s vintage Enco. My center height from the compound is 1", and while some resources suggest a BXA (aka 200) will work fine, the LMS chart shows (correctly in my opinion) that the minimum center height is 1" and change. Comparing the BXA to AXA (aka 100) holders on the Shars website shows that at a 1" center height you cannot fully take advantage of the larger tooling in many cases. You cannot use the cut-off holder at all, it's too tall. You can remedy all of this with modifications, but I'd suggest that the AXA size is plenty robust for the size of the compound on that lathe. Some might also suggest that the BXA could be less rigid in some situations because it hangs the tool further beyond the compound and cross slide. I try to keep my compound backed off to the point where the tool is inside the cross slide whenever possible.


            • #7
              When I was looking to build, I found a couple of people rebuilding theirs due to the dovetail being worn.


              • #8
                I have an 11" Logan and an AXA works just fine for most things but I also have a BXA set for some larger tools

                I don't use the BXA much because it is a little on the large side
                Guaranteed not to rust, bust, collect dust, bend, chip, crack or peel


                • #9
                  I used an AXA setup on my 12" Grizzly lathe; it fit well and worked great. Having "upgraded" to a BXA now on my 13" Jet, I agree with the other comments that it's just a little too large for the 12" lathes.

                  I don't recall ever thinking with that 12" Grizzly that I wished the tool post were larger.


                  • #10
                    The current 4 way tool post is a on my lathe has a base of 3"x"3" and the tools sit 1/2" off the slide.


                    • #11
                      Originally posted by outlawspeeder View Post
                      The current 4 way tool post is a on my lathe has a base of 3"x"3" and the tools sit 1/2" off the slide.
                      But what is the distance from the top of the compound where the tool post mounts to the spindle axis? Again this is crucial to picking the right model of tool post. And also what size tool bits or insert holders do you typically use? These two will tell you how much "tool holder" you can have under the tool bit and that tells you what maximum size holders and thus post you can use. The base size really doesn't mean much. It's being able to hold the cutting edges at the right height.
                      Chilliwack BC, Canada


                      • #12
                        The BXA or 200 size toolholder sets the base of the tool at 1/2 off the topslide. The AXA or 100 is just 1/16 lower. Not a lot in it. The BXA holder has a 5/8 slot but that isn't really so you can put a 5/8 shank in it. However there are always some who want to buy a big tool.
                        The 9249 has a centre over topslide height of 1 3/16. So even the big tool will find he has 1/16 space.
                        The centre of the BXA piston is at 1 3/8 (assuming it is midway up) so above the centre, and the AXA is at 1 1/8 so not a lot in it.


                        • #13
                          What about some of the shanked parting-off tools such as the one at left in first pic, and bottom in second? They have considerably larger shanks than most cutters.

                          CNC machines only go through the motions


                          • #14
                            This is the important part.
                            Originally posted by baz
                            The 9249 has a centre over topslide height of 1 3/16. So even the big tool will find he has 1/16 space.

                            Every Aloris style tool post that I've seen has the tool holder above the topslide. Some designs have it over the topslide all the time, others have it over the topslide only when you have the post set to some angle other than 90 degrees. This sets the lowest that the holder can go.

                            Given that it will only go as low as the topslide surface, the critical measurement becomes the thickness of the bottom part of the tool holder pocket. That is the "A" dimension minus the "B" dimension on page 4 of the aloris catalog ( ) The AXA tool holder has a 7/16 inch thick bottom and will hold up to 1/2 inch shank. If used in the 9249 you should find the cutting edge of a 1/2 inch tool will be on center when the holder is raised 3/16 above the topslide.

                            If you use the BXA instead, the bottom is 1/2 inch and the largest tool is 5/8. That still leaves the cutting edge at 1-1/8, just below the center of axis, so that should work too.

                            If you are using 1/2 inch tools, there is no significant advantage to the use if the a BXA instead of a AXA. The BXA has a larger contact area ( 1/2 inch wider) with the topslide, so it might be stiffer, but the tool is hanging off the side where it's further from the central mounting bolt, so that may reduce that stiffness.

                            Wedge VS Piston: Position repeatability makes a difference when using inserts. You want to be able to remove the holder so that you can rotate the insert to use a fresh corner. You then want to be able to put the tool holder back on and have the cutting edge in the same spot.

                            The wedge does repeat a bit better. The cutting forces push the toolholder back so both surfaces of the leading dovetail meshes. The wedge does the same thing, pushing the holder away from the work and thus preloading the tool in the same position that the work forces would have. The piston style pushes the tool holder away from the body so that one surface of the leading and trailing dovetails bear the pressure. I can put pressure on the front of the holder (shifting it back) as I engage the piston and it will lock it in that position. That can be several thousandths of an inch different from the last time it was mounted.

                            At the end of the project, there is a profound difference between spare parts and left over parts.

                            Location: SF East Bay.


                            • #15
                              Agree with Dan, that extra 3/16" over center height compared to mine makes the BXA conveniently usable on this machine compared to mine. The standard AXA cutoff tool holder is limited to 1/2" and the available insert parting holders only hold a 3/4" blade, so the BXA does have an advantage there, but to take advantage of that I'll guess you'll have to pay close attention to keeping the compound drawn back as close to over the cross slide as possible.