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  1. #1
    Join Date
    Mar 2014
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    1131

    DIY Lathe, bed leveling question

    I just started my epoxy granite lathe project. The bed for the rails is 30x30mm square steel. Would you recommend leveling the bed before or after the casting?

  2. #2
    Join Date
    Jan 2008
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    1523

    Re: DIY Lathe, bed leveling question

    How are you going to level it?

    Are you stress relieving the steel? Epoxy would have to happen after heating for stress relieving.
    7xCNC.com - CNC info for the minilathe (7x10, 7x12, 7x14, 7x16)

  3. #3
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    Mar 2014
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    Re: DIY Lathe, bed leveling question

    Hi pippin,

    I don't have a large grinding machine or a mill to level the bed. So I'll have to get the leveling done in a shop. My lathe is 1.5 meter long so the machine that will be used to level the bed will be large as well. Any suggestions?

  4. #4
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    Jan 2008
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    1523

    Re: DIY Lathe, bed leveling question

    I presume you are casting epoxy granite within a steel tube?

    If you are having it milled or ground, I would pour the epoxy granite before. This is not based on any evidence or experience however, just what I think makes sense.

    Epoxy does not handle heat, so epoxy has to be done after any process involving temperatures near or above the limit for the epoxy.
    7xCNC.com - CNC info for the minilathe (7x10, 7x12, 7x14, 7x16)

  5. #5
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    Mar 2014
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    1131

    Re: DIY Lathe, bed leveling question

    No, I made the mold from plywood. Added the 30x30 square steel bed (or base for the rails?) to the place on the bottom.

  6. #6
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    Mar 2014
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    1131

    Re: DIY Lathe, bed leveling question

    So, if I drill the holes before I heat it for stress relieving, will it get bent?

  7. #7
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    Jan 2008
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    1523

    Re: DIY Lathe, bed leveling question

    I don't understand what you are actually asking.

    If you are putting steel blanks in the epoxy granite, I don't think you need to stress relieve. I don't see how you can 'level' the rails before casting, apart from having an accurate mold (some people have used surface plates).

    If you are welding, then you will need to stress relieve.

    Can you post a picture / drawing of the design? Or a similar machine?
    7xCNC.com - CNC info for the minilathe (7x10, 7x12, 7x14, 7x16)

  8. #8
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    Mar 2014
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    1131

    Re: DIY Lathe, bed leveling question

    Hi,

    OK I have very quick but ugly drawing for you. : )

    I have 50x20mm steel bars for the rail. I'll get them pre-drilled for the rails. BUT I'll also weld some bolt like metals to them for better holding/rigidity. These bolts will be covered with EG.

    My question is will the bars get bent after heat treatment (for stress relieving)? If yes then the alignment of the holes will also be circular and the rails wont get bolted to the bars.
    Attached Thumbnails Attached Thumbnails Untitled-1.jpg  

  9. #9
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    Mar 2014
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    1131

    Re: DIY Lathe, bed leveling question

    Just started to draw my design.

    Now I have 2 options:

    1- Weld the bolts and the block together.
    2- Tap the holes to the half and screw down the bolts very strongly.

    If I choose the first option then I'll need to get it stress relieved.

    If I choose the second option, do you think it is a good idea? Anddo I still need to get it stress relieved?

  10. #10
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    Mar 2014
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    Re: DIY Lathe, bed leveling question

    My real problem is, the total length of the lathe will be 150cm and I don't know if I can find a big mill or a machine to get the whole surface flattened perfectly. So I'm trying to find a way that no surface milling/grinding (to get it flatt) would necessary.

  11. #11
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    Jul 2014
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    215

    Re: DIY Lathe, bed leveling question

    Through a combination of hand scraping and lapping you can get the flatness you need without a mill. You can get it even better than all but the most expensive mills can do. However, it is harder to do with two slim steel rails.

    I think it would be better to tap the bolt anchor holes also and then bond them in place by coating the threads with epoxy. Then you won't have to worry about heat treating which can be very expensive.

    Though it will cost more money, I would suggest an alternative building method to make it easier to make without machine tools.

    I would make the beam one big monolithic beam and embed the steel under the EG by an inch or so. You can use foam dowels to keep EG from filling it the threads. Then you have a larger flat surface of EG that you can lap by hand much like a surface plate.

    It will take more EG to build but will be stronger and have more mass and be easier to get flat. Then you just install the rails right on the EG and bolt them down into the steel reinforcement.

    You can still make some recesses between the rails for chips and coolant to fall into. Just make them smaller.

  12. #12
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    Mar 2014
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    Re: DIY Lathe, bed leveling question

    Hi,

    I don't understand what you mean with "big monolithic beam". If you are suggesting to embed the same blocks under the EG, yes, this sounds much more easier and I like it actually.

  13. #13
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    Jul 2014
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    215

    Re: DIY Lathe, bed leveling question

    Quote Originally Posted by Azalin View Post
    Hi,

    I don't understand what you mean with "big monolithic beam". If you are suggesting to embed the same blocks under the EG, yes, this sounds much more easier and I like it actually.
    I will try to explain what I mean. If you look at your model of the rail bed you will notice all of the empty space and cutouts between the two rails. I know this is how most lathes are made as it allows
    the casting to be made more uniform in thickness and also lightens the rail bed since large solid cast iron castings would be really heavy to deal with. It also allows chips to fall down into a pan and coolant also between the rails.

    Now if you can give up some of this empty space which is used for chips falling and coolant falling and braces between the two main rail bed sections, you could make the rail bed beam almost a solid homogeneous EG material. And make it stronger too.

    Now suppose you had the entire rail bed as just one simple continuous sold beam about the same size as you have designed with the steel rail mounts under 1-2 inches of EG and a few ports for coolant to fall. You would not have as good chip handling
    but for a home machine this might be a good trade off to make the rail bed easier to get real flat.

    So what I am driving at is that you have a nearly continuous unbroken surface of EG on the top of the beam with maybe a few small holes for coolant draining. And you can hand work this and lap it just like they do a surface plate to get it very flat.

    You can make a lap out of some frame reinforced mild steel with a thinner piece of aluminum bonded to it. The aluminum is softer and holds the grinding powder better than steel. Or if you can find an old cast iron lap yo could use that.

    You would need a small granite surface plate to do it. About 18 x 12 inches in size. At that size they are not too expensive. You can buy a cheap grade B China made and lap it yourself to a grade AAA plate with a lap and a little diamond paste. There are several videos on youTube where they show how to scrap in a flat surface. I think it could be cast pretty flat to start with and the EG should work down a lot faster than steel would.


    This is the approach that I am going to take when I build my lathe if I ever get to build it. (Unless I can thin k of something better).

    Best of luck on this project.

  14. #14
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    1131

    Re: DIY Lathe, bed leveling question

    Hi,

    Good idea. But I forgot to mention, I'll use tail stock and I need a shank on the lathe to lock the tail stock. Just like we did on our old manual lathes. I was thinking about your idea. If I use a complete top then it's not going to be easy to lock the tail stock. At least I don't know the easy way. I'm open to suggestions on this.

    My second idea is not to use steel blocks to mount the rails. Instead, I can cut some these pieces you see in the render. These parts will be drilled and tapped so the rails will be siting on the EG surface.

    Also, I added these 10mm thick steel plate with triange cuts inside the EG. May help the rigidity. I can get this plate cut with a laser cutter or a water jet.

    What do you think? Am I still dreaming? : ) I'm saying because I'm about to give up.
    Attached Thumbnails Attached Thumbnails 4.jpg   5.jpg   6.jpg  

  15. #15
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    Re: DIY Lathe, bed leveling question

    I think what you've got is a good design and close to what I meant. I think if you keep the middle slot small enough. It need not be more than 2-3 inches wide. Then you could still have a continuous enough surface area to get a good lapping and have an under surface ledge for the tailstock. There is another option though to consider. You can have a third internal steel support running down the middle of the beam similar to the rail supports to which you can bolt an low profile section of I beam to have as the tailstock tightening surface. I think either way would work. One gives you better stiffness and mass and the other has better chip handling. You can decide which priority is the most important to you.

    By the way if you built it the way you have it modeled I think it would work very nice. It also makes it easier to design the carriage because the tailstock tightener is out of the way. I think that you are close to a really good design. I only wonder if the ledge where the tailstock would tighten should be a little thicker. Are those embedded nuts for the rails to bolt into. That would be a cheap and easy way to do it.

    You could also weld them to the main internal steel reinforcement frame in some manner to really unify the strength of the whole thing.

    EDIT: This is kind of the original idea that I had. Shown without the rails and showing how you could do the tailstock tensioner.
    Attached Thumbnails Attached Thumbnails Lathe rail bed quick concept_1.jpg  

  16. #16
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    Mar 2014
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    Re: DIY Lathe, bed leveling question

    Understood.

    You are right. I don't need the middle space that big. I'll make it narrower.

    I was thinking about the internal construction. It can be also made of construction steel rods. Weld them together and get a nice construction but the whole thing must be stress relieved as well because the wlding, right? Whatever! That's just an option. I'll continue to my design and will share the render files here.

    Thanks Hezz for your help. Really appreciated.

  17. #17
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    Mar 2014
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    Re: DIY Lathe, bed leveling question

    Hezz,

    I see in your render you kept the area small between the two blocks. May I ask the reason?

    Small progress on the design. The plate of the carriage is 10mm thick steel. Is it thin for the machine? Maybe 15mm?

    By the way, the plate will be longer because the rails will be mounted to it.

  18. #18
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    1131

    Re: DIY Lathe, bed leveling question

    .
    Attached Thumbnails Attached Thumbnails 9.jpg  

  19. #19
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    Jul 2014
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    215

    Re: DIY Lathe, bed leveling question

    Quote Originally Posted by Azalin View Post
    Hezz,

    I see in your render you kept the area small between the two blocks. May I ask the reason?

    Small progress on the design. The plate of the carriage is 10mm thick steel. Is it thin for the machine? Maybe 15mm?

    By the way, the plate will be longer because the rails will be mounted to it.
    In my render I do not show the rails. The narrow steel section was just a method for doing a tailstock tensioner which would be between the rails.

    I was just being lazy. The render show a surface mount tailstock tensioning plate.

    Edit: here is the modified render. The central section between the rails is just for the tailstock tensioner. But is surface mounted into the EG.
    There are gaps under the edges to allow a clamp to run under them.

    I also did some design work for a hybrid manual/CNC lathe that I might build in the future. Here is the render and in a way it might be similar to what you are working towards.
    Attached Thumbnails Attached Thumbnails Lathe rail bed quick concept_1.jpg   Hybrid Battle Lathe Assembly_1.jpg  

  20. #20
    Join Date
    Oct 2010
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    1189

    Re: DIY Lathe, bed leveling question

    Hi we do this kind of lathes but with cast steel bed ,.. but nice design is there a reason why you spindle I so far away from the rail ? And how do you intend to drive the Tailstock?


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