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IndustryArena Forum > MetalWorking Machines > Benchtop Machines > 10"x12" Scratch built lathe
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  1. #1
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    10"x12" Scratch built lathe

    Hey Forum,
    I'll start off a new thread about the evolution of my lathe. I started the project about 4 years ago on my high school graduation gift: a 9x20 Grizzly lathe. First it was a VFD spindle,

    then it was a Gecko G540 conversion. At that stage noise was faulting the system and the stock pan was leaking horribly.

    So I started mostly from scratch and built a stand from 1" square tube.

    Then I built a control box where all the wires were shielded and grounded.

    The sliding door was no good so I built a gull hinged door for easy access to the whole machine.

    And these are the two posts. Not enough room for gang style tooling in this machine.

    All the sheet metal was from some guys kitchen floors that I managed to get for a case of beer.

    So after everything is finally running beautifully I get a job for some 1018 steel parts that the machine can not handle. I'm only getting paid about $7per and it's taking the better part of a half hour to turn 1.25" bar stock to an M12x1.5 thread 20mm long. The motor running the spindle is 3hp run off a Lenze/AC Tech VFD, but anytime I run a deeper cut than .02Dia I have to wear earplugs. I tried reinforcing the spindle with some angle iron, but all to no avail. The spindle is correctly preloaded, all bolts are correctly tightened, and the height on all tools is positive with perfect center alignment.
    If you've got some ideas about what's wrong please let me know.
    I need to be able to cut steels(including stainless) and do it in a small production setting. ~100-200 parts.
    So now I'm redesigning the machine from the base up with linear guides, my own 8position turret design, and preferably a D1-4 spindle. I'm shooting for a slanted bed a bit like this lathe.
    All of it should fit inside the enclosure I've already spent a lot of time fabricating.
    I've already got the design for the turret, but I need to find a good D1-4 spindle before I start designing the bed, ways, etc.
    Does anybody know where I can find one that doesn't cost an arm and a leg?
    Thanks for the help.
    Jake

  2. #2
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    Based on the time it is taking to cut such a small amount of material, it could well be that you are feeding way too slowly. Speeding that up might well get rid of all of the screech and chatter. Also, you don't mention what tooling you are using.
    Normally I would have suggested flex in the tool post on a 9x20 lathe as that is a crippling weak link on the machine as I am sure you know, however you have clearly upgraded that weakness very nicely already. Impressive sheet metal work too.
    LongRat
    www.fulloption.co.uk

  3. #3
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    Jake, I don't know what you mean by an "arm and a leg" (i.e. what your price range is), but spindles are expensive. You can fairly commonly find 5C collet spindles on eBay from firms like Dunham. They'll be circa $700-900, but should be very nice spindles with sealed precision bearings and so on. If that's too much, you will probably have to look at making your own spindle.

    I have toyed with that idea, even the idea of making one based on bronze sleeve bearings, which would be a lot easier machining job. In the end, I bought a Dunham spindle, which I intend to use for a 4th axis project.

    Best,

    BW
    Try G-Wizard Machinist's Calculator for free:
    http://www.cnccookbook.com/CCGWizard.html

  4. #4
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    Great looking machine, good job!

    You didn't mention the spindle speed or SFM...too fast perhaps? Can't imagine how a .02 mm (or inch) diameter cut could cause any problems whatsoever in 1018 unless it's WAY too fast?

    Also what does "the height on all tools is positive with perfect center alignment" mean. Perfect center alignment I understand but positive height?

    I have a converted Denford ORAC which is similar to yours in size & construction (except mine has 3/4 hp DC spindle motor) and it'll peel off a decent sized hunk of swarf without a whimper. It's a work in progress and I haven't worked it hard yet. So far the biggest loads I've thrown at it were .060" (dia.) roughing cuts in 3/4" dia. 1018 without a problem.

  5. #5
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    Quote Originally Posted by LongRat View Post
    Based on the time it is taking to cut such a small amount of material, it could well be that you are feeding way too slowly. Speeding that up might well get rid of all of the screech and chatter. Also, you don't mention what tooling you are using.
    Normally I would have suggested flex in the tool post on a 9x20 lathe as that is a crippling weak link on the machine as I am sure you know, however you have clearly upgraded that weakness very nicely already. Impressive sheet metal work too.
    Thanks for the suggestion LongRat. I did forget to mention the tooling. I'm using a Sandvik CCMT3251 PF 4215 grade insert. It's in a 1/2" holder that's choked all the way up in the toolpost. I started with the recommended feeds and speeds off the box at .014" radial depth of cut, .004"/rev and 1500SFM. My machine about exploded with chatter with these values so I took it down to the absolute minimum of .004"DOC, .002"/rev and 1500SFM. Still lots of chatter. The spindle is moving relative to the cross slide, but I tightened every bolt and even built some L brackets to help stabilize the headstock.
    The only way I can stop the chatter is at 200SFM, .01"DOC and .oo2"/rev. The part takes 26min at that speed, and I need to make it in 3. The insert is rated to 1950SFM(15500RPM at .472"diameter), .079" radial depth of cut, and .009"/rev. The insert will get me there even for a finishing mid grade insert, it's the machine that won't.

  6. #6
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    Seems to me you're expecting an inexpensive, notoriously flexible, hobby lathe to do the work of an expensive tool room lathe. Seems extremely unlikely to me a 9x20 will have the rigidity to exercise that Sandvik tool to anywhere near it's maximum capability.

    Regards,
    Ray L.

  7. #7
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    Quote Originally Posted by BobWarfield View Post
    Jake, I don't know what you mean by an "arm and a leg" (i.e. what your price range is), but spindles are expensive. You can fairly commonly find 5C collet spindles on eBay from firms like Dunham. They'll be circa $700-900, but should be very nice spindles with sealed precision bearings and so on. If that's too much, you will probably have to look at making your own spindle.

    I have toyed with that idea, even the idea of making one based on bronze sleeve bearings, which would be a lot easier machining job. In the end, I bought a Dunham spindle, which I intend to use for a 4th axis project.

    Best,

    BW
    Bob,
    Thank you very much for the help. I think I might be able to buy a Grizzly 12x24 spare part spindle for about $600. I'll have to figure that one out, there's no detailed drawing, and it just falls into the arm and leg category. I'll keep an eye on ebay and check in with the local tool distributor to see if there's an old 13 or14-40 lathe for super cheep.
    Quote Originally Posted by DICKEYBIRD View Post
    Great looking machine, good job!

    You didn't mention the spindle speed or SFM...too fast perhaps? Can't imagine how a .02 mm (or inch) diameter cut could cause any problems whatsoever in 1018 unless it's WAY too fast?

    Also what does "the height on all tools is positive with perfect center alignment" mean. Perfect center alignment I understand but positive height?

    I have a converted Denford ORAC which is similar to yours in size & construction (except mine has 3/4 hp DC spindle motor) and it'll peel off a decent sized hunk of swarf without a whimper. It's a work in progress and I haven't worked it hard yet. So far the biggest loads I've thrown at it were .060" (dia.) roughing cuts in 3/4" dia. 1018 without a problem.
    Thanks for the compliment,
    I posted a quickreply before I noticed new posts. I meant positive rake on the tool. Not positive height. You know I might just try replacing the bolts for the headstock with stainless bolts. That might help a lot.

  8. #8
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    Quote Originally Posted by SCzEngrgGroup View Post
    Seems to me you're expecting an inexpensive, notoriously flexible, hobby lathe to do the work of an expensive tool room lathe. Seems extremely unlikely to me a 9x20 will have the rigidity to exercise that Sandvik tool to anywhere near it's maximum capability.

    Regards,
    Ray L.
    Howdy Ray,
    I'm not expecting the 9x20 to perform anywhere near a machining center. I can put these parts on my Tormach and helixmill/threadmill the parts in 4 minutes. I think my lathe should be able to do the same. And now understanding the flexibility of the machine, is why I'm looking for a spindle. I plan to build an entirely new machine that fits inside the enclosure. Something that has at least a 1.25 through bore and a D1-4mount. Also something that's designed with the turret in mind. I appreciate your input.
    Jake

  9. #9
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    Hi Jake

    As Ray stated before those figures were only ever intended for large rigid commercial machines. In your case the tool needs to be loaded up a tad more and the sfm dropped heavily , try keeping the sfm between 200-300, Up the DOC to .05" (diameter) and the feed around .005"/rev. If it can't do this I will be surprised
    I have a 7x 12 mini lathe that will take a 2mm cut (.078") in free cutting steel on 1" diameter bar just fine. Just another question how far does your job hang out from the chuck?
    Nice build by the way!

    Cheers Brayden

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    Hello all,
    I'm sorry I guess I wasn't very clear at what info I was seeking. I'm really just looking for info on D1-4 spindles. Manufacturers, and or build threads on design and construction of a spindle.
    I appreciate all the help with the cut, but my machine just will not remove the material I need. I run a prototype business and everything I make is one off. The problem is that sometimes a prototype requires many turned parts. I never intended my 9x20 lathe to serve as a turning center, but the machine is not meeting a reasonable expectation for turning. So a redesign is in order. I will basically design a new machine that drops into the enclosure I've already built. It will include a turret and tailstock.
    So if anybody has some good info on D1-4 spindle builds that would be awesome. I'll keep this build updated as I make progress.
    Thanks for all the help,
    Jake

  11. #11
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    Seems strange, I would think that there is something fundamentally wrong and probably hasn't got anything to do with the modifications you have made. Even an unmodified manual 9x20 machine should be able to do better than this. I would hunt down the cause of this issue before building an entire new machine, that may not be necessary.
    LongRat
    www.fulloption.co.uk

  12. #12
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    Very neat packaging.

  13. #13
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    Quote Originally Posted by D.L View Post
    Very neat packaging.
    Thank you D.I.

  14. #14
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    the 9x20 lathe is an extremely flexible package and by that I mean not rigid. there are ways of making it stiffer. I have in the past taken way more than your cutting on my 9x20 lathe however there are plenty of areas that need to be addressed.

    1. spindle preload. make sure you preload the spindle really well. if its flopping around you will have no hope of cutting anything
    2. carriage stiffness. make sure that the carriage clamps are tightened and that its not flopping around
    3. cross slide stiffness. this has a pretty crappy gibb, so make sure that you tighten all the screws and they are making good contact.
    4. make sure your spindle is aligned to the ways and not cutting a taper.
    5. make sure your tool nose is on center of just below.


    these are just a few of the areas that I have found that need to be addressed. also I didn't see what HP vfd and motor you have, but your spindle belt maybe slipping under higher load.

  15. #15
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    Update:
    I bought a spindle. It's bigger than the lathe.

    It's a D1-4 with a 55mm bearing surface in the front, and 50mm in the back. I've come up with a design for a new lathe that will machine a 11"dia x 10" and fit inside the existing enclosure.


    I have a couple of questions though:
    The first is about bearings. I've been reading the cncbookbook miniblog on belt drives and I've landed on grinding my own duplex bearing set out of plain angular contact bearings. Mostly because I can't afford a $1500 set of bearings. I don't really know how to figure out what the preload should be and then the amount to grind to achieve it. You'd think that in mechanical engineering school they'd go over things like tolerances or preload, but no.
    Second question; What ABEC rating to go with. The current lathe only spins up to 4000rpm so the bearing rated speeds are well above that. How much will an ABEC 3 bearing change the quality of the lathe over ABEC 7?
    And one more: Aluminum or Steel for the headstock? I was thinking of making the spindle into a cartridge but two bearing supports line bored isn't sounding all that bad. Thanks to everyone lending a helping hand.
    Jake

  16. #16
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    You might have to make a timber pattern to cast an adaptor, bit of a mismatch to sort out there.
    Wisdom results from foolishness!

  17. #17
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    I found some of the info I needed.
    Bearing preload is a calculation based on the manufacturers spec. I found the tables and equations from an NSK angular contact bearing engineering manual. The equation is: Gm= f*f1*f2*Ga. Gm is the Preload. Ga is preload before mounting(in table), f is bearing factor(table), f1 is correction factor based on angle, f2 is correction factor depending on preload class. Example: 7211DS matched angular contact bearing from MRC, f=1.35 f1=.95, f2=1 Ga=330N or 74lbf thus preload should be 95lbf or 423N.
    Next is Fit: The shaft fit for 55mm is +-.00015 and fit on housing is +.0003-0.0
    This is going to be a tricky project. Challenge accepted.

  18. #18
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    Jake, I think you'll find a little experimentation will help with the preload as well. By all means, start with the calculated values and try to figure the spacing needed for that. I believe I have the spacing info in the article you referenced.

    Then you'll want to assemble the spindle and test it while keeping a careful eye on bearing temperatures. You'll want to be sure that's possible and that the bearings aren't buried too well in the headstock to access them. Make sure you're using good quality grease, like the Kluber I reference. Follow the run in procedures you find in the various bearing manuals, again monitoring temps. Once you've run in a bit and temps are stable, you can see whether you've got the bearings too tight or too loose based on the temperatures you're getting. See my spindle article for details.

    Best,

    BW
    Try G-Wizard Machinist's Calculator for free:
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  19. #19
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    Nice build and modeling.

    In post #7 you mention replacing the bolts with stainless to gain strength and or rigidity. Stainless though great for corrosive environments is not very strong, how about grade 8 bolts?

    Also with the new design you have presented and the new spindle, a little more Z would be nice. Seems like a lot of effort to be limited by a 10" piece.

    You are doing great.

  20. #20
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    for this spindle build i would use tapered roller bearings. i have them in my 13x40 geared head lathe using the same spindle. there is a massive thread here on cnczone on spindle construction, bearing preload is the least of your worries. the housing itself will need to be ground and the seats need to be straight and perpendicular to the bearing and concentric and paralle with each other. also you don't have to grind the bearings themselves you can use hardened spacers between the bearings that are ground to create the clearance you need. it will be easier to grind these than to try and keep the bearings clean. abec 3 bearings will be just fine for your build and you won't notice any decrease in performance.

    i think your going to find that constructing the housing for the spindle will be a fairly difficult task and i do wish you all the luck and will offer any advice during your construction.

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