Lathe Steady Rest

New Home Forum Random or Off Topic Lathe Steady Rest

This topic contains 53 replies, has 8 voices, and was last updated by  Bill 4 months ago.

Viewing 24 posts - 31 through 54 (of 54 total)
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  • #84307

    Dui, ni shuo de dui
    Participant

    Using rubber wheels doesn’t seem like a good idea to me, but otherwise it’s a nice design.

    #84310

    Bill
    Participant

    I warned about my drawing skills. πŸ™‚

    20190117_215117

    1 user thanked author for this post.
    #84313

    Bill
    Participant

    The wheels aren’t really rubber, skate wheels are much harder than that. They should have very little give to them, yet have enough that they won’t mar the wood pinched between them. I will, of course, do lots of testing with cheap pool cues before attempting anything with my good ones. πŸ™‚

    Here’s a good one, from RichQ, vintage mid 70s…

    20190112_160948

    That has a double full splice butt, giving eight points. Lots of inlays, including some more complex than squares and dots. It was their top model for the year, though they did simplify it some for the next year.

    #86074

    Bill
    Participant

    And I’ve tried drawing it myself using Inkscape, which just hammers into my head again how much trouble I have with drawing… I also found I’m going to have to tweak a bit from perfect. The center of the lathe is 9.5″ from the table, the top of the pipe is 3.5″, which gives us the 12″ piece size defined for this model lathe. The problem is that if the outer stand is 13″ outside and 7″ inside we’re going to overlap the pipe by an inch. So … we need to cut away that inch at the bottom, meaning we likely want the pivot holes for the arms at 45Β°, 135Β°, 225Β° and 315Β° to make sure the arm doesn’t hit the pipe. We are also likely to have the arms curved toward the center at full retraction, again so they don’t hit the pipe (it might work to have them straight as well). We then need the inner ring to be designed so that it’s outer diameter is less than 13″, likely 11″ instead. Since it’s pivot points are 1″ off the inner edge it won’t interfere with the pipe. Because the main piece has that bit cutaway at the bottom we can’t put a spring down there, so we’ll likely use three springs to give the return tension (they should be just off relaxed when the wheels touch in the middle, so there is always some tension). We need fingers sticking out to hold each end of each spring on both the outer stand and the inner ring and we need the spring fingers on the inner ring to miss the pipe. We may find ourselves dealing with springs rubbing on arms but at first glance I don’t think it’ll be a problem.

    #86099

    Josh
    Participant

    I have been picking at this and I think three rollers would be better mainly because it’s easier to set the points of contact.Β  Do you want to be able to steady a 12″ workpiece in this?Β  Do you know what size the rollers will be?

    #86226

    Bill
    Participant

    With four rollers we can have each pair on a different plane, so they can get down to the minimum spacing (they can actually all touch in the middle with zero spacing, though of course they’d have issues spinning in that case). With three rollers you have them 120 degrees apart from each other, so with the three petals in their minimum position there will be a gap sized by the wheel diameter. IIRC when I did the calc for that skate wheels were too big to get the spacing down to 10mm or under, but lets see for real. πŸ™‚
    The wheels Ryan offers in his shop for the Low Rider are 60mm diameter. There are smaller wheels available, but even the small wheels used on traditional skates are 50mm or larger. Soddy’s circles equation tells us for three identical circles (curvature y = 1/radius x) placed to each is tangent to the other two, the center and outer circles tangent to all three (radius s) are defined such that (3*y+s)^^2 = 2*(3*y^^2+s^^2). So, with x=30 we have:

    (1/10+1/s)^^2 = 2*(3*1/900+1/s^^2)
    150s^^4+3000s^^3+15000s^^2=100s^^4+30000s^^2
    50s^^4+3000s^^3βˆ’15000s^^2=0
    50s^^2(s^^2+60sβˆ’300)=0

    Now ignoring the special case where s=0 and using the formula for quadratic equations that gives:
    s=4.641016 or s=βˆ’64.641016
    or the inner circle at just under 7 9mm, which meets our spec.
    That looks like it either works or I can no longer do math. πŸ™‚ Maybe Ryan will take three wheels, set them next to each other and do a sanity test.
    I don’t see the need to do 12″, that would require the petal/arm to use nearly no width around the circle, mechanically that would give very little to no leverage to the petals and I’d be afraid the vibration would be enough to overcome the spring tension. Hence my suggestion of an inside diameter of 7″ with the petal pivots to the inner ring at 8″ diameter. We can do close to half the full range there.

    #86230

    Bill
    Participant

    Though I suppose if we changed the design to have 16″ outer diameter and 12″ inner diameter we could cut a slot in the table and arrange things such that the arms and petals don’t quite hit the pipe, allowing for a full 12″ part…

    Not quite high on my list, I think. πŸ™‚

    Oh, and your design there is missing the arms. Arms sit between the outer ring and the clockwise edge of the petal, the counterclockwise side of the petal pivots on the inner ring. Four pivot points in total for each petal/arm combo.

    I’m thinking of something like this and this for the pivots.

    #86231

    Ryan
    Keymaster

    hold
    IMG_20190128_125044

    The OD of the spacer is 10.5mm and would easily work. I have a tapered pen and it seems to catch at just a hair under 10mm. You probably need to stagger the top one a tiny bit to be safe.

    #86238

    Bill
    Participant

    Thanks Ryan! Just what the calc actually said. I shouldn’t have been using my ‘rule of thumb’ calc all this time.

    #86239

    Ryan
    Keymaster

    I saw equations and got the chills, cold sweats, panic set in….straight to CAD and I felt better.

    #86240

    Bill
    Participant

    Heh, I start with the cold sweats and such when I open the CAD program… To each their own I guess. πŸ™‚

    #86260

    Jeffeb3
    Participant

    Well… I didn’t read all the responses before I went to onshape…

    screenshot-2019-01-28-1548714836

    #86274

    Bill
    Participant

    Wow, Onshape got the same answer I did, probably a lot faster too, though it wouldn’t have been for me. I’d have had to Google for 45 minutes or so to figure out how to draw the first circle. πŸ™‚

    #86278

    Jeffeb3
    Participant

    Wow, Onshape got the same answer I did, probably a lot faster too, though it wouldn’t have been for me. I’d have had to Google for 45 minutes or so to figure out how to draw the first circle. ?

    Yeah except…

    Now ignoring the special case where s=0 and using the formula for quadratic equations that gives:
    s=4.641016 or s=βˆ’64.641016
    or the inner circle at just under 7mm, which meets our spec.

    7mm != 4.64mm*2… So close!

    #86349

    Bill
    Participant

    Just over 9mm, which meets our spec. πŸ™‚

    So, I ordered wheels and bearings from Ryan, and the pivots and thrust bearings from Amazon. I think if I use an appropriate Loctite on the threads I won’t needs thrust bearings on the outsides… Or maybe on just one outside.

    Now, are the pivots screws/nuts going to interfere with the spacing between the four layers? I’m thinking the base to arm link is spaced by the thrust bearing, the arm to petal is also spaced by the thrust bearing, and the petal to ring is spaced by the final thrust bearing.

    #86354

    Bill
    Participant

    So, current BOM looks like:
    Cut Pieces
    1) Base *2
    2) Ankle *2
    3) Outer Stand *1
    4) Arm *3
    5) Petal *3
    6) Inner Ring *1
    Hardware
    7) Pivot nut and screw *9
    8) Thrust Bearing *9
    9) Wheels *3
    10} Wheel Bearing *6
    11) Wheel Axle *3 (carriage bolt and nut, M8 or 5/16?)

    Am I missing anything obvious at this point? Will I need a spacer between the wheel and petal? I’m working off the assumption I can have a square hole in the petal and use a carriage bolt to hold it, with a minimum of 2″ diameter, less the bolt hole I believe it’ll be unlikely to break away. No real side forces unless things go horribly wrong, and in that case I’ll be too busy calling 911 (or staring at the hole in the garage wall, and in the neighbor’s truck, and their garage, and …) to worry about the breakage. πŸ™‚

    #86365

    Bill
    Participant

    And onward, I chose to purchase some M8 carriage bolts, in various lengths to likely fit the need, as well as flanged nylon lock nuts to match. I figure the flange will potentially work a bit better for holding to the inner race of the bearing. Specs call for a square hole 7.5 mm on a side, but since the round bolt portion is M8, it might be better to use an 8mm square hole:

    Head style: Carriage
    Head height Min: 4.12mm
    Head height Max: 4.88mm
    Square width Min: 7.42mm
    Square width Max: 8.58mm

    I believe the Square width max number to be the diagonal across the square… Note the bolt head height is under the 5mm used by the thrust bearings, so we shouldn’t drag until we actually hit the inner ring. Maybe we should mount the wheels on the outer stand side of the petals? That might allow retraction to the full size of the inner ring instead of stopping when the wheels hit.

    #86485

    Bill
    Participant

    Anyone know anything about springs? I’m going to need to source them and decide how they will best mount. I’m thinking eye bolts into the outer stand and inner ring with the springs tying them together It might take a bit of fanegaling to best place them so they don’t interfere with the arms…

    #87605

    Bill
    Participant

    Still waiting on the thrust bearings and pivot bolts, but I picked up some Home Despot springs that might work. I also got what looks to be appropriate eye screws, they have 1/2″ screw depth and 1/2″ eye. I’ll add them to the eventual BOM.

    #96205

    Josh
    Participant

    Bill have you gotten any hardware?Β  Going to be laid up for a while

    #96224

    Bill
    Participant

    I have what I believe to be all the hardware and a friend has been working on the drawings for me. He uses Corel Draw though, so it’s not quite CAD worthy. He’s also trying to change the design on me in several places and I have to argue to get them back to my design. ;(

    IrisFinal

    Note that in this ‘final’ design he has the petals opening backwards, trying to push the wheels open while the lathe is spinning counter-clockwise. The positioning of the arms also forces the maximum size to be smaller, but at least that’s wide enough for my needs. One suggestion we came up with that works is the order of the layers. I had said outer, arm, petal, inner and what actually should work better is outer, petal and inner, arm. That should have a bunch less slop when assembled. With the inner circle flush against the outer we could add some bearings to act as rollers around the outside. Note that when I say ‘flush’ I really mean ‘a thrust bearing depth apart’. πŸ™‚

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    #96227

    Bill
    Participant

    Looks like the board glitched on me and generated two posts. So this one is not the same as the previous one. πŸ™‚

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    #96238

    Jeffeb3
    Participant

    Bill, it sounds like you’ve got a good project to get serious about learning CAD. You’ve done the hard work on the design, now just figure out how to use the tools.

    #97238

    Bill
    Participant

    Yeah, I get three or four hours in to learning how to do it in a CAD program, then get frustrated and set it aside. My mind really doesn’t want me to be doing CAD… πŸ™

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