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metalmagpie
11-30-2011, 01:26 AM
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?

danlb
11-30-2011, 01:45 AM
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

terry_g
11-30-2011, 01:53 AM
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

wierdscience
11-30-2011, 02:07 AM
They do it to make an otherwise perfectly good lathe bed less rigid.

.RC.
11-30-2011, 02:20 AM
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...

The Artful Bodger
11-30-2011, 02:20 AM
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.:)

gnm109
11-30-2011, 02:24 AM
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.

Dr Stan
11-30-2011, 02:27 AM
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.

JRouche
11-30-2011, 02:29 AM
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

Ian B
11-30-2011, 02:44 AM
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

hardtail
11-30-2011, 02:48 AM
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.......

philbur
11-30-2011, 03:02 AM
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:)

darryl
11-30-2011, 03:06 AM
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.

mike4
11-30-2011, 03:22 AM
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

Ian B
11-30-2011, 03:53 AM
Darryl,

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

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

Evan
11-30-2011, 04:23 AM
The rigidity of a lathe is measured by the length of the loop through the effective neutral fibre of the mass of material from the cutting tip of the tool to the point on the work it touches. That loop passes through the tool, the tool holder, the top slide and cross slide, the carriage, the bed, the headstock, the spindle, the chuck and the work piece.

With a gap bed lathe the length of that loop is dramatically longer than with no gap. Even with the gap piece in place it cannot be as effective as solid metal.

If we add enough metal below the gap to maintain the same total cross section as we have with a lathe with no gap we gain nothing in stiffness. The stiffness goes down with the increase in the length of the working loop. This is a result of scaling laws.

In order to increase stiffness enough to compensate for the longer working loop the entire extra length must have the cross section doubled. This means the mass must increase by the increase in cross section multiplied by the extra length of the working loop.

To win back the rigidity lost by the gap requires a huge increase in the amount of mass based on the usual increase in length of the working loop. Of the gap bed lathes I have seen most do not come close to making up the loss of rigidity. It isn't easy to do since there is limited space to add the required extra mass and economical restraints also play a large part.

DATo
11-30-2011, 05:12 AM
Simple belief I follow : The more tool versatility you have in a shop the more you can do. My 13 X 40 is a gap bed and I admit I've never used that feature yet but I'm glad it came that way.

Better to have and not need than to need and not have.

jugs
11-30-2011, 05:47 AM
As Evan says, (post 16) it's all to do with stiffness, you've ether got it or you haven't (all determined at conception)


:)

......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
.

In stress terms that isn't a gap-bed, its a straight bed with 2 carriages piggy backed
http://www.youtube.com/watch?v=RAnJe0aTiks&feature=related

sliding gap bed lathes are useful in jobbing /repair shops & where space is at a premium like a ships w/shop BUT what you gain in versatility you lose in amounts of metal/rev that can be removed compared to a similar full length straight bed machine.

Ian B
11-30-2011, 06:13 AM
The OP's original point wasn't about rigidity, but the (perceived) difficulty of replacing a gap properly after it has been removed. Given sensible levels of cleanliness, is there any specific reason why proper realignment should not be achieved?

Because if there is, then we could equally argue against ever removing the headstock chuck that the lathe came supplied with...

Ian

.RC.
11-30-2011, 06:29 AM
I doubt this gap bed lathe had much of a problem with lack of rigidity..

http://www.lathes.co.uk/purcell/page4.html

flathead4
11-30-2011, 08:43 AM
Even if a particular gap-bed is less rigid than its non-gap cousin, if it is rigid enough for your purposes then it makes no difference. Except in these discussions, of course.

Tom

justanengineer
11-30-2011, 09:06 AM
If there was no need for gap bed lathes, or many worries about their rigidity, I doubt they would exist. Ive only ever used one, without the necessity of using the gap, and had no issues. I wouldnt mind having one given the choice.

I also doubt that if there was no need for gap bed lathes, there wouldnt be so many standard bed lathes out there with "gaps" hacksawed out of them.

duckman
11-30-2011, 09:14 AM
We had a TOS 22X ? with a gap and it was taken out probably once a month, if it didn't have the gap there were jobs we would have had to send out to other shop, biggest piece was 34" and the chuck jaws cleared by 1/2", when I put the gap piece back in all surfaces were wiped with my bare hand feeling for dirt or chips.

bborr01
11-30-2011, 09:15 AM
I have a 18X40 gap bed lathe. I have not had a need to use it as a gap bed yet, but if the need arises I will not hesitate to remove the insert.

My lathe is a very solid machine and I have never had any rigidity issues with it. I think a lot of rigidity issues with gap bed lathes are from the lathes being light duty in the first place. These same lathes would probably have rigidity issues with or without the gap bed.

Brian

H380
11-30-2011, 09:50 AM
http://i786.photobucket.com/albums/yy145/H380/photo-2.jpg

#2 to #3 bell housing adapter ring. The problem was the gap was too large. I could not get close enough to the chuck with the carrage. I made Boring bars out of 1 1/4 inch bar and used HHS cutters. It started out as a Plasma cut ring out of 3/4. You can see the chatter marks. But it worked.

gwilson
11-30-2011, 10:03 AM
My 16" lathe has a gap. I removed it once to swing a 24" job and made $600.00 on that job. I wouldn't have been able to make that money without the gap feature. It is perfectly rigid enough with the gap feature. I suppose the bed is massive enough in the first place,though it is a Grizzly.

The main thing to be careful of is to get everything PERFECTLY CLEAN before you put the gap back in,or it won't QUITE fit perfectly,causing problems.

I want the feature. We had the same model lathe at work before we got the 18" Promaster. The gap was removed several times for work there. It is most useful when needed. The difference between doing a job and not being able to handle it.

daryl bane
11-30-2011, 10:19 AM
I have a old Enco 12x36 Gap bed. One of the things that I have been concerned with in taking out the gap is, was the casting clean when they assembled and ground it at manufacture? I can certainly make sure that it will be clean when it goes back in, but I would be really mad to see swarf, paint etc in the virgin mating joints.

lazlo
11-30-2011, 10:29 AM
A gap bed is an insurance policy, its a waste of money until you need it.

A properly design gap bed lathe, like the Mori Seki or Dean Smith & Grace toolroom lathes, has massive bed around the gap section. They're so ridiculously rigid, removing the little (in comparison) gap makes no difference in rigidity.

This is the gap from a Mori Seki 1250 toolroom lathe. 3,7000 lbs. Tell me there's a rigidity issue :p

http://www.nsmachine.com/11940_4.jpg

gwilson
11-30-2011, 10:31 AM
I might add this: FEW new lathes go SLOW enough to turn large pieces that must go into the gap. My 16" I modified to turn 30 RPM,but that is still way too fast. You need more like 5 or 10 RPM for really large gap bed work.

A VFD would be in order if you have a 3 phase lathe.

Fortunately,my 24" job was a maple forming block for hammering a silver tray into. If I did a lot of large diameter work,I'd modify the lathe to run at half the 30 RPM it runs at now. I had built in an extra 2 step pulley to get it to run as slow as it does,because factory slowest speed was 60 RPM,which is ridiculous for a 16" lathe,let alone gap work.

I don't need the highest speed to be as high as factory was. Small jobs I do in my HLVH. The best plan would be to buy a 3 phase lathe and put a VFD on it. When I bought this lathe,VFD's weren't as common,or as cheap as they now are.

Davo J
11-30-2011, 10:34 AM
I say it is just a myth.
Grizzly and other lathe suppliers are not helping the situation, because they in their manuals that their is no warranty claims if you remove the gap bed and it wont fit back in properly, as it was machined in place. So people will continue for years to come thinking they cant remove it.

I have a 12 x 36 and the gap has been out plenty of times to do things like fly wheels, drum brakes and large jobs. I have had guys in my shop that have been shocked by the thought of it, because their manual warns against it. This is why I bought a gap bed lathe, to fit the occasional large job.

I always clean it and the lathe properly, and while tightening the bolts and inserting the taper pins, I place a mag base on the carriage and run the indicator along from the bed way onto the gap way. I do this on the top and one side of the V way at the front and the flat way at the rear. It has always measured up 0.00 on the dial indicator when I have replaced it, and expect it always will.

Dave

lazlo
11-30-2011, 10:37 AM
My "Properly Designed" comment obviously doesn't apply to Chinese lathes ;)


Grizzly is not helping the situation, because it has in their manuals that their is no warranty claims if you remove the gap bed and it wont fit back in properly, as it was machined in place.

Wow, that's crazy! How can you sell a machine and claim the warranty is void if you use a key feature?!

radkins
11-30-2011, 10:46 AM
All the pros and cons aside I use the "gap" in my 14x40 quite often and if rigidity, with the gap piece in or out, has been a problem I certainly haven't noticed it, and this is with a HF lathe! I repair a lot of mining equipment parts and a lot of this stuff requires the extra clearance but one job in particular requires the gap piece be removed each time so repeated removal does not seem to be a problem either. These are very bulky and heavy parts but so far they have been no problem at all and I could not have done them without that gap, so why do they make a gap bed lathe? Because it's handier than a shirt pocket! :D

jugs
11-30-2011, 12:58 PM
A properly design gap bed lathe, like the Mori Seki or Dean Smith & Grace toolroom lathes, has massive bed around the gap section. They're so ridiculously rigid, removing the little (in comparison) gap makes no difference in rigidity.

This is the gap from a Mori Seki 1250 toolroom lathe. 3,7000 lbs. Tell me there's a rigidity issue :p

http://www.nsmachine.com/11940_4.jpg

Can't see a gap, someones bolted a lump of iron in the way :D


The addition or removal of a gap block in a gap bed makes no difference to the strength/torsion/rigidity of the bed, it is to allow the carriage full support as it approaches the headstock.

A bed casting with a gap in it is not as strong as a similar size bed with no gap!!

One problem with swinging oversize work is once the tool is outside the bed the line of cutting force is not straight & the carriage tries to tilt away from the work - giving chatter, we used to load the back edge of the carriage with lead blocks to counterbalance the forces.

Evan
11-30-2011, 01:03 PM
The OP's original point wasn't about rigidity, but the (perceived) difficulty of replacing a gap properly after it has been removed. Given sensible levels of cleanliness, is there any specific reason why proper realignment should not be achieved?

The original post is all about rigidity since it is the lack of same that causes problems with replacing the gap piece. When the lathe is installed it will only take a slight bending moment caused by a twist in the bed or a change in the configuration of the lathe compared to how it was configured when the gap piece was originally fitted to cause a problem.

The claim by the manufacturer that the piece was "machined in place" is misleading. While that may apply to the bedway surfaces it cannot apply to the mating surfaces of the gap piece. You cannot simply saw out the piece to produce the gap piece. All methods of cutting remove a kerf. It must be a separate part fitted to an existing gap in the ways. Both mating surfaces must be separately machined to an accurate fit in the gap. The configuration and alignment of the lathe at the time of the fitting will largely determine how well the piece fits later.

Any change in that configuration including not only the alignment of the bed but even the position of the carriage and tailstock (or their existence) will affect the fit of the gap piece. It is the reduction in rigidity that directly affects and increases the importance of later lathe alignment so that it matches the alignment when the gap was fitted. Any deviation that closes the gap in the slightest when the piece is removed will make replacement difficult or impossible. Just the weight of the carriage on the bed may be sufficient to cause a problem if the carriage and tailstock or equivalent weight wasn't in place when the gap was fitted.

Ideally, the factory will set up the lathe as if it were installed for use and configured as such before fitting the gap piece. While that is certainly how it is done by the better manufacturers it is hoping for too much to expect that from low cost mass produced machines.

It is the trite but true "everything is made of rubber" principle at work. In this instance it is the very feature in question that adversely affects the rigidity which may make the feature problematic.

Carld
11-30-2011, 01:28 PM
I won't argue the structural integrity of the gap bed lathe because I am not a structural engineer. What I will argue is I have used several gap bed lathes and have removed the gap part several times and have never had an issue of getting them back in perfect alignment. As long as your meticulous about getting every mating part clean and bolted and pined as required.

The gap bed I have at home has had the gap removed several times with no problems of misalignment. Also, the lathe bed is in perfect alignment with the headstock which tell me this 1983 lathe has not suffered any sagging or misalignment of the bed due to having a gap bed construction.

Could that be that it was correctly designed?? You think???

wierdscience
11-30-2011, 01:49 PM
Our 24x120 at work is of the typical Eurotrash/Asian design,square box head stock and a gap bed.When they did the gap they used four 18m socket head cap screws and two taper pins for alignment.It isn't much trouble getting it back in place,but it isn't as simple and plunking it back in and tapping the pins in either.

The single biggest gripe I have against gap bed lathes is the width of that gap is fixed and most of the time is too wide.On the lathe at work with the gap removed it is 22" to the edge of the topslide with the carriage legs fully supported by the bed.even if the whole length of the gap is used there is still 10" of tool overhang.

Essentially what you have is a way to pull off the odd over sized job with cobbled up,greatly overhung tooling.So we end up with a feature that is used less than 10% of the time that affects performance for at least some percentage of the rest.

For the record I do like sliding gap lathes as the gap can be set back for just what is needed and not what they give you.Pay attention to the carriage design on that Leblond sliding gap that Hardtail posted.The crosslide is designed so it's offset all the way to the headstock side of the carriage.

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

gwilson
11-30-2011, 02:17 PM
I don't have the manual of my grizzly 16" handy (1986 purchase). If they are saying that the gap piece can't be gotten back in perfectly,it may just be a way of covering their rear ends. I have had no problem getting the gaps back in the 2 Grizzlys I have had. They may be anticipating that some users may not get the lathes perfectly clean before re assembly.

Other than that,I can see no reason why they'd make a statement like that. If you can't get the gap to fit back in,it would just be better to leave the feature off.

Some lathes,mine included,and I think most modern lathes,have the inside ways stop a little short of the head stock. This allows an area where workpieces larger than the lathe's swing,and not very wide,to be swung. A guy I knew had a Howa lathe,and it had no removable gap,but that little extra area "saved" him a few times,allowing a large piece to be swung in a pinch.

radkins
11-30-2011, 02:27 PM
I don't have the manual of my grizzly 16" handy (1986 purchase). If they are saying that the gap piece can't be gotten back in perfectly,it may just be a way of covering their rear ends. I have had no problem getting the gaps back in the 2 Grizzlys I have had. They may be anticipating that some users may not get the lathes perfectly clean before re assembly.

Other than that,I can see no reason why they'd make a statement like that. If you can't get the gap to fit back in,it would just be better to leave the feature off.

Also some people suffer from "bubba" syndrome and if the gap piece does not just fall into place then maybe a few taps with a hammer will will get it unstuck! :rolleyes:

boslab
11-30-2011, 02:32 PM
i cant honestly understand the fear of removing the gap piece, thats what its for, i regularly use the gap on my harrison, havent had a problem yet, i suppose its all about confidence, once you get used to it its second nature, btw how many of ur REALLY work to tenths lol, mostly were mangling to thous! if were lucky
be brave, its there to be used
mark

Mcgyver
11-30-2011, 03:12 PM
The obvious answer to the OP's Q is unless you're making steel mill rolles, when the envelope is pushed you may need a lot of length, or a lot of swing, but rarely at the same time. Cynical answer is marketing.


For the record I do like sliding gap lathes as the gap can be set back for just what is needed and not what they give you.Pay attention to the carriage design on that Leblond sliding gap that Hardtail posted.The crosslide is designed so it's offset all the way to the headstock side of the carriage.

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

what an awful video, i think i feel seasick! :D

Leblond is now made in china, If you want a really nice sliding gap bed, Standard Modern makes one here in Toronto that is quite something. Basically goes from a 21x36" lathe to a 36x54 - centre distance increases as well when you open it up (or longer). 7.5 hp, Nice lathe. I've been through the plant at a very high level of detail - these lathes are made as nicely as any 1st world lathes; everything is made here including the castings, make all their own gears, leadscrews, parts are scraped, etc. Neat operation.



sliding gap bed lathes are useful in jobbing /repair shops & where space is at a premium like a ships w/shop BUT what you gain in versatility you lose in amounts of metal/rev that can be removed compared to a similar full length straight bed machine.

just a function of design and construction quality, the above mentioned is a very rigid 7.5 hp lathe, expanded or closed. Mating of the sliding bed to fixed bed would have to be done properly. They are more money though

macona
11-30-2011, 03:20 PM
Our Colchester Mark 1-1/2 at work is a gap bed. I have never had a problem getting it in place nor rigidity issues.

lynnl
11-30-2011, 03:42 PM
The rigidity of a lathe is measured by the length of the loop through the effective neutral fibre of the mass of material from the cutting tip of the tool to the point on the work it touches. That loop passes through the tool, the tool holder, the top slide and cross slide, the carriage, the bed, the headstock, the spindle, the chuck and the work piece.

With a gap bed lathe the length of that loop is dramatically longer than with no gap. Even with the gap piece in place it cannot be as effective as solid metal.

If we add enough metal below the gap to maintain the same total cross section as we have with a lathe with no gap we gain nothing in stiffness. The stiffness goes down with the increase in the length of the working loop. This is a result of scaling laws.

In order to increase stiffness enough to compensate for the longer working loop the entire extra length must have the cross section doubled. This means the mass must increase by the increase in cross section multiplied by the extra length of the working loop.

To win back the rigidity lost by the gap requires a huge increase in the amount of mass based on the usual increase in length of the working loop. Of the gap bed lathes I have seen most do not come close to making up the loss of rigidity. It isn't easy to do since there is limited space to add the required extra mass and economical restraints also play a large part.

I won't pretend that's all clear to me. :)

But it sounds like another way of saying "bigger is less rigid," or "for max rigidity, use a lathe barely big enough." ???

Evan
11-30-2011, 03:53 PM
But it sounds like another way of saying "bigger is less rigid

Not quite. Rigidity does not scale linearly with mass, it scales with area (cross section). That is why there are limits on the sizes of everything from animals to mountains. It applies to machines as well. Doubling the mass does not double the rigidity. Doubling the rigidity increases the mass by the 3/2 power.

At some point, depending on the strength to weight ratio of the material, the increase in mass overtakes the yield strength of the material. That is why planets are spherical.

lynnl
11-30-2011, 04:57 PM
Well, I'm (vaguely) interpreting that statement "...length of the loop through the effective neutral fibre of the mass of material ..."
to mean the line of points lying between all the compression forces on one side and tension forces on the other.

Seems to me that line MUST always be longer with larger machines.

In other words, I think there must be additional factors that need stating.

I'm not refuting your statement; as I've implied, it's not at all clear to me.

tdmidget
11-30-2011, 05:46 PM
Leblond is now made in china, If you want a really nice sliding gap bed, Standard Modern makes one here in Toronto that is quite something. Basically goes from a 21x36" lathe to a 36x54 - centre distance increases as well when you open it up (or longer). 7.5 hp, Nice lathe. I've been through the plant at a very high level of detail - these lathes are made as nicely as any 1st world lathes; everything is made here including the castings, make all their own gears, leadscrews, parts are scraped, etc. Neat operation.



just a function of design and construction quality, the above mentioned is a very rigid 7.5 hp lathe, expanded or closed. Mating of the sliding bed to fixed bed would have to be done properly. They are more money though

You never reported on your visit to S-M to PM. But LeBlonds are not made in China, they don't list any new lathes. If S-M is such a going concern, why did they sell their parts division to LeBlond? How could they possibly build 30 models in that tiny plant? What became of the saale offer?

Mcgyver
11-30-2011, 06:07 PM
But LeBlonds are not made in China, they don't list any new lathes.

not so, from a link on their web site

http://www.leblondusa.com/LinkClick.aspx?fileticket=P37oY%2bmjQrc%3d&tabid=38

I phoned and the person i spoke confirmed they are made are offshore - to correct my original statement I can't remember if it was China or Taiwan but it was Asia


You never reported on your visit to S-M to PM. If S-M is such a going concern, why did they sell their parts division to LeBlond? How could they possibly build 30 models in that tiny plant? What became of the saale offer?



I discontinued my interest, no idea the current status...not speaking out of school as they posted publicly that they were looking for a buyer.

How big a plant does it take to make a lathe? They don't inventory much. but they do everything in house. Lots of false reports around about them bringing parts from china bolting them together here - I believed them myself. That is absolutely 100% false. These lathes are of high end manufacture - they do all the things you're supposed to do. All the lathe castings are made in Canada and stress relieved, they have every conceivable type of gear generation machine, a huge German leadscrew thread miller, planers and way grinders than can take up to 20' beds, very large vertical and horizontal cnc machining centres, etc etc. The only thing they don't do in house is pour the cast iron and flame harden the beds; send out for that. Fitting is high end, all done by hand scraping.

I made/make no comment as to how much of going concern they are, only that the product and process seem first class with no dirty secrets like fronting for offshore supply. As to why they outsource the parts, perhaps to minimize overhead. It is lean and mean. The proprietor comes out of operations, front end isn't his thing. imo that aspect of how they run their business is a strategic blunder, giving up the margin and distancing yourself from the customer, just my opinion.

thistle
11-30-2011, 06:40 PM
I took the gap out of my lathe, to swing a large iron wheel, and havent had it back in for a couple of years, as i keep getting things to that fit the gap...
also i have a turret that i mean to cut a groove in to fit said lathe, and mean to use the gap piece to gauge the bottom of the turret.....
maybe one day i will get it back in.

wierdscience
11-30-2011, 07:11 PM
The obvious answer to the OP's Q is unless you're making steel mill rolles, when the envelope is pushed you may need a lot of length, or a lot of swing, but rarely at the same time. Cynical answer is marketing.


Probably all marketing,one company does a poorly executed gap bed and the rest follow suit.A big improvement would be if they simply offset the cross slide on the carriage so the god awful overhang is diminished.

As for rigidity,this 10,000lb 20hp lathe shudders and chatters in ways it really shouldn't given it's dimensions and the best explaination for it is the 8" deep 20"long notch they made in the bed for the gap:)

Toolguy
11-30-2011, 07:13 PM
To me it seems that the type of stand it is bolted to would make a difference. For example, sheet metal versus heavy cast iron. I think a good stand could do a lot of stiffening.

Arthur.Marks
11-30-2011, 07:28 PM
I had a good need for a gap not long ago---and it had nothing to do with rigidity. My largest lathe swings 8" diameter, and I had to make a plate which was 12.5" diameter. The large flange was only a 1/4" thick, though, with a circular hub. It was a straightforward milling job with a rotary table, except it needed a smaller, long section with a keyed bore attached. I had to send it out to be welded. I was dreaming of a gap because then I would have just cut a nice, left-hand, fine pitch 2" thread on the OD of the central hub. The machine the part fit spun the disc in one direction only. It would have made a nice connection. No CNC here so no possibility of thread milling it. A gap would have fit the bill nicely.

Evan
11-30-2011, 07:54 PM
Seems to me that line MUST always be longer with larger machines.

Yes, most often it is. But in a larger machine the length of that line increases in only 2 dimensions while the mass of the larger machine increases in 3. The problem arises when the length of the loop is increased but the mass of the machine doesn't in the proportion that it does in a larger machine.

This is all a result of scaling laws. When something is scaled up or down various aspects of material properties do not scale at the same rate. Scaling up in just one dimension scales mass linearly, area linearly, cross section not at all in two dimensions, and scales stiffness down in inverse proportion. Scaling up in just 2 dimensions scales mass and area by the square of the linear dimensions while stiffness remains the same. Scaling up in 3 dimensions still scales area by the square but mass by the cube so stiffness scales by 3/2 power.

Scaling in 3 dimensions increases mass faster than it increases stiffness. Stiffness still increases but not as fast as mass so eventually a point of diminishing returns is reached which limits the size of structures using the same materials and geometry. When you make a lathe larger it must be made more massive than would result by simply scaling the dimensions of a smaller lathe. These scaling rules can be ignored to some extent for small scale factors such as the difference between a 10 inch lathe vs a 12 inch lathe but they become very important when you double the size of a machine.

Introducing a gap in a 10" machine so it can accept 20 " work does not make it a 20" lathe. If scaled proportionately a 20" lathe will weigh 8 times as much as a 10 inch lathe.

Evan
11-30-2011, 08:01 PM
I think a good stand could do a lot of stiffening.

It most certainly can. A stand is part of the lathe, not just a place to support it.

I have my SB9 bolted to a large chunk of channel iron. That greatly increases the rigidity.

Ignore the gold plated ways. :D It's just the lighting.

http://ixian.ca/pics9/lathe_mount.jpg

rdfeil
12-01-2011, 01:05 AM
I have a 17X40ish LeBlond Regal sliding gap machine manufactured in 1951. With the gap slid open I can spin a 38 inch flywheel with no problems. I can open the gap from 0" (closed) to 30" and still take a .250 deep cut in stainless easily - - No rigidity problems here. It is nice to be able to slow the spindle down to less than 10 RPM for the big stuff. It is really nice to be able to just slide the gap open as little or as much as is needed for the job, then close it up for day to day use.

hardtail
12-01-2011, 02:16 AM
Nice size, your swing basically doubles and the slide takes care of all the issues of still being too far away........that lathe was a great design.....

Davo J
12-01-2011, 03:15 AM
I don't have the manual of my grizzly 16" handy (1986 purchase). If they are saying that the gap piece can't be gotten back in perfectly,it may just be a way of covering their rear ends. I have had no problem getting the gaps back in the 2 Grizzlys I have had. They may be anticipating that some users may not get the lathes perfectly clean before re assembly.

Other than that,I can see no reason why they'd make a statement like that. If you can't get the gap to fit back in,it would just be better to leave the feature off.

Some lathes,mine included,and I think most modern lathes,have the inside ways stop a little short of the head stock. This allows an area where workpieces larger than the lathe's swing,and not very wide,to be swung. A guy I knew had a Howa lathe,and it had no removable gap,but that little extra area "saved" him a few times,allowing a large piece to be swung in a pinch.


Here is a link to one manual, it's on page 70
http://cdn0.grizzly.com/manuals/g0709_m.pdf

They have manuals online for all there current lathes, so there might be one close to yours.

Dave

philbur
12-01-2011, 03:28 AM
Of course the detrimental effects of scaling can be greatly mitigated by an intelligent use of the material, but then that's probably the difference between a lathe manufacturer who really understands what he is doing and one that doesn't.

With a gap bed lathe you only need to compensate for the loss of rigidity at the gap, you don't need to increase the overall rigidity.

Phil:)

Davo J
12-01-2011, 07:00 AM
One thing I have noticed is that some gaps are wider than others. I have a 12 x 36 Chinese lathe that has a decent size gap, but when I went to a friends place I noticed his 12 x 40 Taiwanese lathe gap was probably 3/4 the width of mine. This would make it limiting or a lot of jobs as some times I run out of room.

Dave

gwilson
12-01-2011, 09:05 AM
Davo,you must have gone through a lot of trouble to print the whole manual!! I had no reason to doubt you,though.

That was a pretty strange statement:" removing the gap is considered an alteration of the lathe". I think they could overcome that problem by grinding the ways with the gap in, removing the gap and re inserting it,and regrinding if needed if it springs out of shape. Probably too much trouble for them,though,at the prices they get for their lathe back at the factory.

Fortunately,I haven't had that problem myself,BUT my Grizzly lathes were both made in Taiwan. I bought 2 in 1986. One for work,and one for home shop. No telling what the Chinese mainland stuff might do. Taiwan machinery costs more,but I urge everyone to go for it if they can afford it.

I ordered a Chinese milling machine for work,and sent it back. The table was WAY to high on the front edge. I can't recall how much too high,but it was way out of spec. A certain amount of bias is o.k.,to allow for tool pressure,but this one was way over. I ended up sending it back,and they made a deal with me for a Taiwan mill. I'll withhold the dealer's name.

The reason I ordered another mill was I wanted a longer table. The original 1986 Taiwan mill is still doing fine at work,and I have its brother at home. It has been so nice that I haven't bothered to play musical machines when good used Bridgeports have become available.

Davo J
12-01-2011, 09:30 AM
Hi,
I didn't scan the manual, I just went to the Grizzly site and grabbed a link to their manual. They have the manuals for down load under most of their machinery.

I only post it so people didn't have to go chasing it up. I am sure one of the other manuals have about warranty because I remember reading it, but just picked that manual because it was smaller as some are 22mb.

Dave

David Powell
12-01-2011, 09:31 AM
The gap in his lathe made a perfect place for him to keep his coffee mug. I can only suppose that the hot chips kept it warm and the cutting oil added to the flavour! regards David Powell.

dominus
07-31-2013, 09:54 AM
Hello everyone

My name is Kyriakos and i m from Greece.

I saw this thread and I couldn't resist to be a member of this forum just to add my story on this urban myth.

Long long time ago when expensive cars have a right side mirror as an extra, dial indicator's was the latest gadget. Every big company have 1 and only the chef engineer was allowed to use it.

Ahhh what a times.... Yes at those times IF you remove your removable part of the lathe you where in BIG trouble. How would you put it back correct?

But the times changes. We have i-everything and dial indicators are for free (well almost...).

This is the setup i use everytime after i remove the gap. No more than 5 minutes to put it back correct.

http://i1291.photobucket.com/albums/b547/dominus164/IMG_3900-2_zpse0526bc5.jpg

Of course proper cleaning and inspection of the surfaces is a must.

So, happy to be here and i hope to forgive my English

Kind regards

Kyriakos

Toolguy
07-31-2013, 10:29 AM
Welcome aboard Kyriakos!:)

bob308
07-31-2013, 10:45 AM
well it seams like the people that have run a gap bed lathe find no problems with them only the armchair experts that have not used one don't like them. do you think the manufacture would design and make lathe that would not make good parts. now keep in mind these lathes were made for industry not the hobby shop.
yes i ran a 16" lathe with the gap out i was treepanning 24" al plates.never had a problem putting the pice back in. this was a common opperation that dap came out about once a week.
my brother rescued a 9" southbend gapbed lathe from the scrap pile. cost him $100. this is the first 9" i ever saw with the gap. heard of one other. i am trying to trad him one of my other 9" s-b for it.

bob308
07-31-2013, 10:48 AM
Kyriakos welcome to the board. your english is way better then my greek. even your spelling has me beat.

Jaakko Fagerlund
07-31-2013, 11:13 AM
I've used two gap beds and both of them had tapered dowel pins to locate them in place. Never had any problems, just wipe the surfaces clean with your bare hand and lower the piece back in, tap in to place, drive the pins in and bolt it down. No need for measuring anything.

MrFluffy
07-31-2013, 01:03 PM
Ive only taken the gap piece out of my harrison a handful of times, but every time I did, it saved my bacon on some weird or awkward job. I used to find it difficult to get a tool right out the rim of the workpiece mounted on my biggest faceplate and ended up with some right bizzarely shaped tools to cut outer edges, but since I fitted a multifix, I can just hold the holder on the opposite side of the toolpost and have at it.

Shade
07-31-2013, 01:59 PM
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.
IIRC we had an 16x72 lathe on our little DD, that gap came in and out
more than a Philippino 'Entertainer' We had to replace a bunch of Hytrol
valve seats and it was a 12 months wait for the parts or something silly
like that we make a fixture welded up the needed parts and had are MR
finish them up. A Hytrol valve seat is a threaded round seat that screws
in to the valve body, but there are 3 spokes that meet in the center for
a small hub that guides the valve disc into place, the OEM parts are machined
from a 316 casting, we fabricated the rough part and then it was machined to fit.


I've used two gap beds and both of them had tapered dowel pins to locate them in place. Never had any problems, just wipe the surfaces clean with your bare hand and lower the piece back in, tap in to place, drive the pins in and bolt it down. No need for measuring anything.

I would love to own a gap bed there are a number of times I really could have used it.

Rich Carlstedt
07-31-2013, 02:01 PM
A 14 inch gap bed lathe will weigh considerably more than it's 14 inch straight bed cousin.
That's because the lathe is beefed up at the gap section.
You don't see this weight variance however in some Chinese Lathes, so this issue is lathe specific
You can argue that it has more flex , but I have never seen it in our DSG's of other gap lathes at work
and it is cheaper than having two lathes for sure in a home shop.
Rich

wierdscience
07-31-2013, 02:58 PM
A 14 inch gap bed lathe will weigh considerably more than it's 14 inch straight bed cousin.
That's because the lathe is beefed up at the gap section.
You don't see this weight variance however in some Chinese Lathes, so this issue is lathe specific
You can argue that it has more flex , but I have never seen it in our DSG's of other gap lathes at work
and it is cheaper than having two lathes for sure in a home shop.
Rich

IF the lathe is properly designed,meaning the bed beefed up,the crosslide is offset towards the chuck,the drive system has an extra low range gear change and the removeable gap is properly keyed and fitted then okay.

Problem is most are not at which point the gap feature is a negative.The modern light weight lathe has little in common with a DSG or a LeBlond.

This is the problem in a nutshell with our 24" gap bed at work.
http://img.photobucket.com/albums/0903/wierdscience/DSCF0002_zpsaddc1805.jpg (http://smg.photobucket.com/user/wierdscience/media/DSCF0002_zpsaddc1805.jpg.html)

With the gap removed and the carriage pads all the way to the edge of the gap it's 22" from the chuck to the topslide.As a result anything that's done with the gap out is done with a cludge that involves a boring bar and a lot of chatter.

IF they had beefed the bed up at the gap(they didn't,or at least not enough)and they had offset the cross slide it would be much more usable.But they didn't and the result is the lathe isn't as ridgid as it could have been.

Jaakko Fagerlund
07-31-2013, 03:14 PM
wierdscience, that lathe pic is a really good example of how to not do it, thanks for showing it :) The one lathe at work that has a gap bed has almost the same issue, not so pronounced, but the carriage front will likely hang out a little if working with a face plate and not a chuck. Isn't so much of an issue as the carriage is 6 times wider than the best overhang, but still leaves a lot of leeway for questions.

boslab
07-31-2013, 03:40 PM
It's a gap bed, it's there to be used, of course it fits back unless you leave a pile of chips under it, clean drop in away to go, even if it was a few tents out it won't make any difference, most of us aren't making space shuttles, go for it, I do agree with the rpm issue, mine goes down to 45 rpm and its still a tad fast when the diameter fills the gap (23"), can throw some scary swarf though!
Mark

Davek0974
07-31-2013, 03:50 PM
I have the gap in and out of my Colchester student all the time, never had an issue lining it up again, just run the fingers along the faces and clamp up, I checked it once with a DTI and it was perfect. The edges of the bed and gap piece are sharp so easy to feel a lip if there was misalignment.

Couldn't do without that lathe.

wierdscience
07-31-2013, 07:57 PM
wierdscience, that lathe pic is a really good example of how to not do it, thanks for showing it :) The one lathe at work that has a gap bed has almost the same issue, not so pronounced, but the carriage front will likely hang out a little if working with a face plate and not a chuck. Isn't so much of an issue as the carriage is 6 times wider than the best overhang, but still leaves a lot of leeway for questions.

Yes,it would have been better without the gap.What good is having 20hp if you can't use all of it ?

The only logical solution is to take a 14"American Pacemaker,add 10,000 lbs to it and make it a sliding gap lathe,it's the only way;)
http://img.photobucket.com/albums/0903/wierdscience/pacemaker-warehouse_zps23f41aca.jpg (http://smg.photobucket.com/user/wierdscience/media/pacemaker-warehouse_zps23f41aca.jpg.html)

tmc_31
07-31-2013, 09:03 PM
This is a great thread. My lathe is a Jet 1340A gap bed. Now, I am from the old school of: If there is a button, push it! If it has a sign that says "Don't push this button" push it faster!! So after reading all the reasons why not to remove the gap plug in my lathe, I had to take it out just to see if I could get it back in right. As it turns out the plug went right back in and seemed to go back into alignment with little fuss. I did not do any work with it out so no swarf was generated. However cleaning it shouldn't be too difficult. It was a worthwhile exercise because I can see a number of ways that this feature can be used.

Tim

firbikrhd1
07-31-2013, 09:33 PM
I believe the "don't remove the gap piece in your lathe bed" idea is about 80% machinist urban legend and about 20% accurate. Most of it depends on the quality of your lathe and some on how ham handed the operator is. My neighbor, a tool and die maker, has a gap bed lathe and he removes that portion of the bed without even batting an eye. His machine is an import but apparently the design is rigid enough and the method used to locate the gap portion repeatable enough that he has no issues with rigidity or accuracy.
Right or wrong, when he replaces the gap portion he cleans the area where it seats to almost almost sanitary condition. He then applies a small amount clean oil and "floats" the gap portion into place where it is located by pins and then bolts it in place. This may not be the "authorized" or official method, but it seems to work nicely for him.

The Artful Bodger
07-31-2013, 10:36 PM
If your gap piece will not come out, or does not want to go back in maybe you have stressed the lathe when bolting it down.

wierdscience
07-31-2013, 11:13 PM
Maybe it's myth,maybe not,all I know is the one I posted,the gap piece weighs 350+lbs.It has four 20mm bolts and two taper pins.
Taking it out is a cheater pipe and pry bar function.Putting it back is a cleaning ritual that if not preformed right always results in some tiny crumb getting knocked out and mucking up the alignment.Pull it back off,repeat steps 1,2 and 3.

A more practical and useful solution is an auxillary headstock and toolpost riser along these lines-
http://www.youtube.com/watch?v=2ivuCRavE8I

It solves the overhang problems,doesn't effect the rigidity of the bed and the speed issue can be corrected with the right gearing.

Rich Carlstedt
08-01-2013, 12:17 AM
IF the lathe is properly designed,meaning the bed beefed up,the crosslide is offset towards the chuck,the drive system has an extra low range gear change and the removeable gap is properly keyed and fitted then okay.

Problem is most are not at which point the gap feature is a negative.The modern light weight lathe has little in common with a DSG or a LeBlond........................................... ....................

This is the problem in a nutshell with our 24" gap bed at work..............But they didn't and the result is the lathe isn't as ridgid as it could have been.

Exactly Right !
The issue isn't whether removing a gap is good or bad , Its really is : Not all Lathes are good with gap beds.
It all depends on WHO made the Lathe.
The example of the Mori or a DSG is great. They know how to make gap bed lathes. ( or American, or Leblond )
The Chinese do not.
This is like arguing if a car can run a race course decently.
One guy has a Corvette, and another guy has a Pinto...Duhhh
You can't make a general opinion off that!


Now as to whether to remove the gap and replace it with precision ?
How many times have I seen vices with chip dents on the bottom ? 100's
How many times have I seen vice jaws with dents behind them ..too many !
And these are the same guys who have problems with gaps..in every case

Rich

Rich Carlstedt
08-01-2013, 12:20 AM
By the way, as Weird pointed out, part of the gap bed design is having adequate cross slide travel/location
and that involves proper design with an offset cross-slide being closer to the headstock.
Rich

1200rpm
08-01-2013, 06:30 AM
in the case of the typical 12x36 from the land of cheap eggs- it does seem a bit silly design-wise to be swinging 17" with a lowest speed of 70 rpm on a machine with a 7.25" wide bed.

i admit i have not used one, but given the choice of gap or no gap on this type of machine i would choose no gap.

i am sure, however, many have used this feature to good effect. :)

Richard P Wilson
08-01-2013, 08:45 AM
I've got an old 6" centre height lathe with a gap that lets me turn work up to 16" dia x 1 1/2" wide, or 4 1/2" wide if I take the gap piece out which I do quite often to turn flywheel castings. No way I've got room in a small workshop for an 8" centre height non gap lathe. Because its old, the speed range is pretty low, 30rpm min as standard, 20 rpm if I change to a smaller motor pulley. Its weakness, and thats one common to a lot of gap bed lathes, is that its tricky to get the cross slide out far enough to turn the edge of a 16" workpiece. It does now, because I've modified it, and modified the keeper plate at the back of the saddle, so it stops the back of the saddle lifting when I'm cutting at maximum diameter.
No, I've never bought into the theory that you shouldn't take the gap piece out. I've done it on a number of lathes, and given close attention to cleanliness, I've had no trouble getting them back in OK. A troubling thought, raised by someone else, is 'what if the original manufacturer got a bit of swarf under the gap piece when the bed was machined in the first place?' Thats a situation I've never come across, and one I'm not going to think about until it does.

Richard

dp
08-01-2013, 03:34 PM
In the oldy days the gap was there but the replaceable ways section was not available. Then somebody thought to make it a removable option. It allows you to have a more affordable machine that can do the occasional odd job that requires more room. Cheaper than buying a much larger lathe that may be too big all the time or a small lathe that is too small some of the time. It also gives you a sweet spot to drop the chuck on and which you can remove and hide when friends are in the shop so they don't see the scars. That's about all that part of my ways is ever used for anyway :). It also sends a quiet message to them and gives you bragging rights that you're turning some big chit. Really big!

krutch
08-07-2013, 03:16 PM
About two months ago I took out the gap on my Clausing to do a job. It was the first time I had pulled it out. It had been out once for a job in my shop way back when, but it was a lathe guy I had working in here that did that. I was unsure how it came out. The manual was of no use to see how it came out. Once it was out by my hands, it was a piece of cake. The dowels on it are tapered and serve to locate and align the gap piece. It must be clean and rust free for a good fit.
I have no pause to remove the gap when needed now.

PeteM
08-08-2013, 12:02 AM
The rigidity issue can be considered this way. First, the rigidity from the tool point down through the carriage to the bed is essentially the same in regular and gap bend versions. Second, the rigidity from the spindle down to the bed is essentially the same. What remains is a question of enough metal to keep the bed sections (headstock end versus carriage end) from twisting with respect to each other -- often with fairly low horsepower cuts. Given the large box section that's left in any decent gap bed design, that's entirely doable.