Gap Bed Engine Lathes - Removing the Gap

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Hi,

I am considering purchasing a 14" -16" engine lathe to fill the gap between my smaller 12" Atlas/Craftsman bench lathe and my larger Nakamura-Tome Slant 1 CNC turning center. I am considering either a used American made machine (South Bend, Logan, Clausing) or a new Asian machine (PM, Birmingham, or a Taiwan built machine).

All of the Asian machines that I have seen have a "gap-bed" design to allow larger diameter parts to be accommodated. I do not believe I have seen any American made machines with this feature. I have the following questions that I hope some of you will be able to answer:

1. I have been told by the local machine tool dealer that it is not a good idea to remove the gap because it is impossible to align it properly when reinstalling it. He says this misalignment will throw of the alignment between the ways and result in loss of accuracy. It would appear to me that if the gap (and as a result the bed ways) were out of alignment (either vertically or horizontally) that this would result in the carriage possibly moving out of its normal alignment as it contacts that portion of the bed ways that are part of the removable gap piece. My question is - do any of you have experience with this problem, and if so how hard is it to realign the gap portion of the bed?

2. It would seem to me that the removable gap feature (even with the gap installed into the lathe bed) would reduce the torsional stiffness of the lathe bed as compared to the same lathe if it did not have this break (gap) in the bed/ways. I would appreciate any thoughts you might have about this.

Thanks,
David


www.deserthybrids.com

[One of Many]

I have seen the gap removed/replaced on a Clausing and it wasn't pretty. Very obvious on used lathes where you can see evidence of wear at the transition line. I can imagine what it is doing to the carriage surfaces.

Any time something precision is machined as an assembly there are built in stresses as in strains, tensions and compressions that cannot realistically be reset in unison. Small and medium size lathe gap beds are a perfect example of that, but sounds good in the brochure list of features. Larger lathes are not normally used as high precision, but the mass of the bed and gap section do not flex as much either.

Sure, it is going to be slightly weaker, but in some respects if the machine is heavy enough, this also allows you to align the bed to the spindle centerline easier as it is leveled to cut true. Otherwise you will need to pull it down to the floor with anchors.

DC

[larry charlton]

I have a gap engine lathe built around 1900 it weighs aproxamatly 3 tons it has a 36 inch face plate it doesnt shift or bend when the gap is removed If you want a gap bed make sure it is heavy and well builtor it will shift when the gap is removed.

[Geof]

A gap bed in a small/medium sized lathe is bordering on pointless. If you do take it out as mentioned you will very likely never get back the original alignment and if you do try machining anything large enough to need the gap you will probably find the machine either cannot go slow enough for the large diameter or is simply underpowered for large diameters.

[One of Many]

Pointless sums it up about right. My Jet 14x40 has the feature, but the carriage would extend into that gap area in order to reach the cutter relative to the compound. Then the carriage fills the gap, dho? Then there is some issue with the chuck extending over the top of the gap, so the part wouldn't swing in there anyways. It tends to be a face plate function only, but good luck with a cutter setup that will reach it.

This would probably apply to Grizzly, Wilton and a few others that re-label the same iron.

I can't complain too much for 25 cents on the dollar and still new! That is about all it was ever worth.

DC

[KENNETH BROWN]

I GOT A HWACHEON 12" CHUCK MANUAL LATHE THAT WE HAVE PULLED AND REPLACED THE GAP BED ON MANY TIMES WITH KNOW PROBLEMS AT ALL.

[Bear]

This is a triky ?
Ive some "machinests "tell me dont
touch/lean, machine while theyr maching
a part too,.Unles that gap is more than half
the length of the saddle (wouldnt the part hit
the charige ?).
took gap out of 24" summit and never saw a
need to replace it.
Bear

[NC Cams]

Lets use some common sense.

Chances are the bed was fully assembled and the ways ground when the machine was at the factory i some state of assembly. God only knows the condition of the surfaces where the gap was fit.

On one mill I boght, I disasembled it to "blueprint" it and found the "precsion machine surfaces" to be decently machined, horrubly dirty and shoddily shimmed. After "cleaiing" things up, it went back togehter but it took quite a bit more "tuning" to get it back right.

It stands to reason that if you took the thing apart, the ground ways would/could NOT realin perfectly - Why? unless the gap were EXACTLY placed where it was and tighteneed EXACTLY the same, simple mechanical delection would/could affect how it would go back togehther.

if you put a dial indicator on the lathe, you can probably lay a hand on the bed and measure SOME deflection - imagine what a twist in the bed or the bolt torquing can/will do.

Would I remove the gap in my gap bed lathe? I have no plans EVER to do so and will shoot the person who even puts a wrench on the heads of the bolts to try to remove the gap......

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I recently came across a copy of the Grizzly Model G0509 & G0509G 16” x 40” owners manual. It says the following:

"Your lathe has a gap section below the spindle that can be removed for turning large diameter parts. The gap is installed, then ground at the factory during lathe assembly for precise fit and alignment. Factors during original lathe assembly apply additional forces to the gap; therefore, replacing the gap to the original position will be very difficult. We don't recommend removing the gap. If removed for turning large diameter parts, reinstallation to exact factory alignment is nearly impossible. The only option is to then leave the gap out and lose carriage travel near the chuck."

Here is the link to the manual:

http://www.grizzly.com/images/manuals/g0509_m.pdf

This would seem to support the idea that it could be very difficult to reinstall the removable gap portion of the bed with these types of lathes.

I also found this information about the Clausing Colchester 15" lathes:

"The bed was 11-inches (280 mm) wide, induction hardened and ground-finished as standard; it was of the usual Colchester V-and-flat type, with separate pairs of ways for the carriage and tailstock, and available in two lengths that gave either 30 or 50 inches (760 mm and 1270 mm) between centers. Both beds could be had either with or without a detachable gap piece that allowed material up to 23-inches (580 mm) in diameter and 6.125 inches (155 mm) thick to be swung on the (optional-extra) 14 and 21-inch (355 mm or 535 mm) diameter faceplates."

The above is a quote from:

http://www.lathes.co.uk/colchester/page21.html

It does not say anything about replacing the gap. I would assume that it might be easier to replace the gap and align it on the Clausing than on one of the Grizzly lathes. I am thinking this may be due to grit, dust, rough casting, etc. between the gap and bed at time of manufacture for the Grizzly. Perhaps the Clausings were finished to a higher level under the gap years ago.

In any case, I am still evaluating and seriously considering purchasing one of the Asian lathes - in particular the Grizzly G0509 or G0509G.

Thanks for all your input.

David