Thanks Thanks:  0
Needs Pictures Needs Pictures:  0
Picture(s) thanks Picture(s) thanks:  0
Page 1 of 2 12 LastLast
Results 1 to 15 of 18

Thread: Spin Test

  1. #1
    Join Date
    Jul 2010
    Location
    Melbourne
    Posts
    9,088

    Default Spin Test

    So I'm working on mounting my rather large TPG to my lathe. The first thing I need to to is scrap the bottom of the TPG mount. The problem is the face I am scraping is not centered. The balance point is at the red line in the picture. What is this going to do to my spin test?

    Stuart
    Attached Images Attached Images

  2. #2
    Join Date
    Jun 2008
    Location
    Victoria, Australia
    Age
    74
    Posts
    5,080

    Default

    Quote Originally Posted by Stustoys View Post
    So I'm working on mounting my rather large TPG to my lathe. The first thing I need to to is scrap the bottom of the TPG mount. The problem is the face I am scraping is not centered. The balance point is at the red line in the picture. What is this going to do to my spin test?

    Stuart
    Hi Stuart,

    If it's way off would it matter? Suppose it's bowed, then the spin test will rotate around an end depending what side you push.

    I guess when you get really close it might be trickier, it will be based on the friction between the part and the plate, that is the product of area and weight, so I guess the center of area rather than the center of gravity would be the reference point?

    Good question..

    Regards
    Ray

  3. #3
    Join Date
    Apr 2013
    Location
    Karana Downs QLD
    Posts
    78

    Default

    Hi Stuart, I dunno what a TPG is and this time, I'm not sure what I'm looking at, but if part of the problem is keeping something out-of-balance under control, then I saw a machinist once who needed to machine a crank with the co-rod still attached (from a Manx Norton). He rigged up an overhead tie point and lashed the rod to it with a bungee cord - worked brilliantly.

    If I'm right off target (likely!) can you show a pic of the wider problem?

    Regards, Daryl

  4. #4
    Join Date
    Jul 2010
    Location
    Melbourne
    Posts
    9,088

    Default

    Quote Originally Posted by RayG View Post
    If it's way off would it matter? Suppose it's bowed, then the spin test will rotate around an end depending what side you push.
    Hi Ray,
    This is the sort of thing I think will happen......... though I wouldn't know.

    Now given there is little chance of me bending the piece, maybe it would be ok to press down on the right hand side and forget the spin test?

    For a bonus point how do I check the the dovetail is square to the base?(bearing in mind it isnt square to the base in the other plane). Though I really doubt it matters much.......

    Stuart
    Attached Images Attached Images

  5. #5
    Join Date
    Jul 2010
    Location
    Melbourne
    Posts
    9,088

    Default

    Hi Daryl,
    TPG=tool post grinder
    I think you are off track, but you have given me an idea. I could bolt a weight to the work piece to even things up.
    I'll try and chase a better pic

    Stuart

  6. #6
    Join Date
    Jul 2010
    Location
    Melbourne
    Posts
    9,088

  7. #7
    Ueee's Avatar
    Ueee is offline Blacksmith, Cabinetmaker, Machinist, Messmaker
    Join Date
    Dec 2011
    Location
    Canberra
    Age
    39
    Posts
    4,515

    Default

    Hi Stuart,
    You need a granite square......
    Surely you could set up an indicator to test a dowel at the top and bottom of the dove.....but you need that square or a master you can run an indicator stand on. The square would have to be set up at 90ded to the flat dovetail ways too....
    Keep in mind there is probably an "easy" way too
    1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.

  8. #8
    Join Date
    Oct 2012
    Location
    Australia
    Posts
    621

    Default

    Quote Originally Posted by Stustoys View Post
    Hi Ray,
    This is the sort of thing I think will happen......... though I wouldn't know.

    Now given there is little chance of me bending the piece, maybe it would be ok to press down on the right hand side and forget the spin test?

    For a bonus point how do I check the the dovetail is square to the base?(bearing in mind it isnt square to the base in the other plane). Though I really doubt it matters much.......

    Stuart
    Square in both axis or just one?

  9. #9
    Join Date
    Jul 2010
    Location
    Melbourne
    Posts
    9,088

    Default

    Hi Josh,
    Thats the problem, As I'm only ever going to get the base I am scraping square to the dovertail in one plane and the slide moves ot an angle to the base on the other plane, measuring squareness is going to be tricky.
    I'm not 100% sure yet it needs to be square anyway. Unless the slide is parallel to the cross slide it will move "side ways*" anyway when moved vertically.

    Stuart

    *towards or away from the chuck

  10. #10
    Join Date
    Oct 2012
    Location
    Australia
    Posts
    621

    Default

    Quote Originally Posted by Stustoys View Post
    Hi Josh,
    Thats the problem, As I'm only ever going to get the base I am scraping square to the dovertail in one plane and the slide moves ot an angle to the base on the other plane, measuring squareness is going to be tricky.
    I'm not 100% sure yet it needs to be square anyway. Unless the slide is parallel to the cross slide it will move "side ways*" anyway when moved vertically.

    Stuart

    *towards or away from the chuck
    I think you are right it does not matter, you just dress the wheel to the angle that you want anyway... Unless I'm thinking about it all wrong...


    It might matter is you are side grinding orthogonal to the first face.. I don't know when you might do that on a lathe though.?

  11. #11
    Join Date
    Jul 2010
    Location
    Melbourne
    Posts
    9,088

    Default

    Hi Josh.
    I was thinking more about if I were grinding to a shoulder. A vertical movement of the wheel(which I am thinking will give me much finer adjustment than the cross slide, though there would be some maths involved) If the slide isn't vertical there would be a Z movement as well as an X movement. But even if I made the base square to the dovetail I would then have to set it up the almost vertical slide of the TPG parallel to the cross slide or there would be a Z movement anyway. I think the slide can be made to move vertically by rotating the TPG base. This would mean the grinder spindle wouldn't be dead parallel to the lathe spindle but as you say, once the wheel is dressed that's not really an issue.
    I think I might shelve the worry about that until I see how well the grinder work on my lathe anyway.
    Not that we would ever try and grind a shaft to dia and a face a shoulder at the same time anyway.

    Stuart

  12. #12
    Join Date
    Jul 2010
    Location
    Melbourne
    Posts
    9,088

    Default

    Well I put the slide and spindle back on which moved the balance point forward to much more like halfway. A light stone(as I'd been playing around with it back on the lathe) and this is how it spotted. It even seemed to even past the spin test!

    Stuart
    Attached Images Attached Images

  13. #13
    Join Date
    Apr 2013
    Location
    Karana Downs QLD
    Posts
    78

    Default

    Thanks for the education of the unwashed Stuart. Now that I know what a TPG is, I should show you mine - its a 125mm angle grinder mounted on the tool post. I popped the diamond dresser in the non-rotating chuck to dress the dished-disk to dress the face. I have not used a stone wheel, but I can't see that as a problem if the grinder is of the trigger variety (either on or off - but not with a vari-trigger) - then hook the grinder to a 10amp Speed Ctrl to wind the speed back. I will get a pic of my heath robinson effort.

    Daryl

  14. #14
    Join Date
    Apr 2013
    Location
    Karana Downs QLD
    Posts
    78

    Default

    This is the 'Daryl-TPG'. I have only used it for very hard materials - but I don't see a problem adapting this method for other materials. The disc in the pic isn't the one I have used for face cuts - I have used this one for longitudinal cuts. Because of the rotation of the grinder, the lathe has run run in reverse.

    The mounting holes and their faces in the grinder housing were done by removing the housing from the grinder and milling/drilling the faces and holes in the mill. The adaptor is fairly solid MS.
    Attached Images Attached Images

  15. #15
    Join Date
    Jul 2010
    Location
    Melbourne
    Posts
    9,088

    Default

    Hi Daryl,
    I think I've lead you up the garden path.
    When I said "stone" I didnt mean the wheel. I meant stoning the base to be sure there were no burrs on it before putting it on the surface plate to blue it for scraping it flat.
    The motor I'm using is 3 phase so it will be running on a VSD* which will give me variable speed.

    Be interested to see your grinder though, I had thought about doing something along those lines but this one turned up for $100.

    Stuart

    *poping in another bunch of letters for you. Thats variable speed drive which converts single phase to 3 phase... clever little box.

Page 1 of 2 12 LastLast

Similar Threads

  1. Scraping, the spin test.
    By Ueee in forum METALWORK GENERAL
    Replies: 10
    Last Post: 5th Mar 2013, 11:07 AM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •