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why do they make gap bed lathes?

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  • why do they make gap bed lathes?

    Everyone I know who has a gap bed lathe always is quick to tell me how the gap piece has never come out, and how they never would ever in life consider removing it. Nobody thinks they could ever get it back in quite right.

    So why do lathe manufacturers bother?

  • #2
    They probably bother because there are uses for it.

    My 9x20 will spin a 7 inch cylinder (over the saddle) but the jaws from the chuck will hit the ways before it is adjusted out enough to grip a 7 inch piece. A gap right where the jaws are would help a bit.

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

    Location: SF East Bay.

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    • #3
      I used to run an old 15" swing Wilson Lathe that had a gap bed. With the gap insert removed and a tool holder I built I could reface 24" diameter brake rotors.
      That is the only thing I ever removed the gap insert for. Getting it back in place was never a problem.
      I have a 12" x 36" lathe with a gap. I have never had occasion to need to remove it but I certainly would if the need was there.

      Terry

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      • #4
        They do it to make an otherwise perfectly good lathe bed less rigid.
        I just need one more tool,just one!

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        • #5
          Originally posted by wierdscience
          They do it to make an otherwise perfectly good lathe bed less rigid.
          Not really as they have a heavier section in that area to compensate...

          The likes of the Graziano lathe has a natural gap...
          Precision takes time.

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          • #6
            Originally posted by wierdscience
            They do it to make an otherwise perfectly good lathe bed less rigid.

            That is so but putting the piece back in makes a quite good lathe better.

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            • #7
              I've removed the gap in my 13 X 40 Enco lathe several times in the years I've owned it usually to make large discs of aluminum plate. It has a large plate with a D1-4 mount that's something like 16" in diameter, IIRC. It will swing a 17" piece with the gap removed. It's held in with two large tapered drive pins and a large socket head screw. It's a worthwhile feature for unusual items.

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              • #8
                Both ships I served on had 24 X 120 Lodge & Shipply gap bed lathes. The one on the Coral Sea (a carrier) may have been used at some point, but not while I was on board for 2 years. The largest work pieces we chucked up were 12" OD aluminum bronze billets from which we made wear rings for the centrifugal fire & flushing pumps.

                The Samuel Gompers had one, but we also had a couple of 60" VTL's which made the removal of the gap redundant.

                During all the years I worked in civilian and academic machine shops I never saw another gap bed lathe.

                So, I guess that leaves me agreeing with Weirdscience.

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                • #9
                  Yeah, I agree with wierdscience. The break in the bed WILL make it disconnected in a way.

                  Lathes without the gap have the head mounted firmly to the entire bed (the rails).

                  A gap bed will be relying on the under structure of the bed to be able to keep the head aligned with the main rails. I havent seen any lathes that are large enough to keep the head aligned with the bed like you can get with a full length bed, just havent seen it, not that its not there.

                  Folks with lathes can have a difficult enough time getting the bed rails set to the head. Toss in the "cut out" and there is even more of an issue.

                  Id rather not have one. JR
                  My old yahoo group. Bridgeport Mill Group

                  https://groups.yahoo.com/neo/groups/...port_mill/info

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                  • #10
                    Gap bed lathes work just fine. If you were to take a straight bed lathe and then mill a gap out, then yes, I could imagine that it'd be weak. But gaps are designed in, and metal is added to compensate. What's hard about that?

                    I normally keep the gap piece in place, as it gives support to the left hand end of the saddle when working near the headstock and protects the gap's mating surfaces. I've removed it, and it goes back in as if it's never been out. Of course you need to make sure it's clean, there are no burrs etc - but it's not exactly rocket science.

                    Having the gap takes the capacity of my lathe up from 17" diameter to about 23" diameter, albeit for short workpieces. That makes the gap about 3" deep.

                    By preference, all else being equal, I'd pick a gap bed over a straight bed.

                    Ian
                    All of the gear, no idea...

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                    • #11
                      I would definately consider and even seek out a gap bed for another lathe, have thought a 16x6/80 with a gap that could swing close to 25" would be ideal........now if I could find one I would go for a LeBlond sliding gap bed, just have to make a hatch in the wall for it to protrude from........

                      http://www.youtube.com/watch?v=VN9vlAFxJww

                      I've heard the argument many times about it not going back together properly, with some rigorous cleaning I can't see reassembly a problem.......unless you left the gap out for years then maybe.......
                      Last edited by hardtail; 11-30-2011, 02:58 AM.
                      Opportunity knocks once, temptation leans on the doorbell.....

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                      • #12
                        A gap bed is an insurance policy, its a waste of money until you need it.

                        You may not know today whether you will ever make a claim, but if you ever need to you're very glad you bought it.

                        Phil

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                        • #13
                          Seems that if the ways were down as low as the gap, and the toolpost was higher to compensate, you'd have the extra capacity all along the bed. Instead of an 8x18, I'd have an 11x18. And if the ways were further apart, you'd have some extra capacity without having to add height (or subtract bottom, as with a removable gap piece). With the ways further apart you'd have a more stable base for the carriage and a longer slide for the crosslide. That would also give you more slide for the compound. What's the catch- the bed would end up being heavier? Aw.
                          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                          • #14
                            Lathe capacity

                            Originally posted by Ian B
                            Gap bed lathes work just fine. If you were to take a straight bed lathe and then mill a gap out, then yes, I could imagine that it'd be weak. But gaps are designed in, and metal is added to compensate. What's hard about that?

                            I normally keep the gap piece in place, as it gives support to the left hand end of the saddle when working near the headstock and protects the gap's mating surfaces. I've removed it, and it goes back in as if it's never been out. Of course you need to make sure it's clean, there are no burrs etc - but it's not exactly rocket science.

                            Having the gap takes the capacity of my lathe up from 17" diameter to about 23" diameter, albeit for short workpieces. That makes the gap about 3" deep.

                            By preference, all else being equal, I'd pick a gap bed over a straight bed.

                            Ian
                            Many times people have said that they need a larger lathe to carry out some larger than normal project , but dont have the space for a full blown machine .
                            Then take the gap out and do the job , clean up and put the piece of metal back in .
                            Not hard if you stop listening to the old wives tales about sagging bedsor it wont ever go back the same .
                            Mine has been removed more times than I care to remember , but like others have said good house keeping is critical , it only takes a seemingly insignifigant piece of swarf to cause it to sit up in one corner.
                            I am presently keeping a look out for a machine with a 3.5 to 4 metre bed and a 100mm spindle hole just to rework some shafts.
                            Quoted about $1800.00 just for one and there are eight of them .
                            Justifies a bigger machine to me .
                            Michael

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                            • #15
                              Darryl,

                              They do indeed make lathes with lower beds, as you describe. They normally call them "bigger lathes" and charge more accordingly!

                              The commonest problem that I've seen with buying secondhand gap bed lathes is that the gap piece (if it ever existed - not all gap bed lathes have gap pieces, just look at the Myford 7's) is missing. Finding a replacement from a similar lathe doesn't look like a good option, as the gap piece is probably ground along with the bed. One from another lathe would likely not fit as it should.

                              Ian
                              All of the gear, no idea...

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