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View Full Version : Gap bed, anybody ever use that feature?



Rusty Marlin
03-17-2007, 08:32 AM
I've got a job that requires I pull the gap on my gap bed.
A machinist at work that I respect highly, says NEVER, EVER pull the gap, that it will never line back up correctly when replaced.

So I'm REAL hesitant to pull the gap and may try to find another way to the job.

So what say yea? Anybody use the gap bed capability?

Charles Ping
03-17-2007, 08:35 AM
Used it once in 5 years - and yes, it was a pain to get back perfectly (well as perfectly as I needed).
Now that I have a better mill & boring head I'd do a similar job on the mill and leave the gap in place.


Charles

Bill Pace
03-17-2007, 08:47 AM
Good question! I've wondered about this also, and always read with interest any ones experience with it. I would guess that I've read maybe 6-10 mentions of doing it, and the ratio is DEFINATELY against! BUT, there were a couple times where the guy says he does it "all" the time and never has a problem....... I think I would be in the group of not getting into it, just kinda makes me cringe at thinling about re-aligning.

John R
03-17-2007, 08:55 AM
I have not had a need to pull mine but I have a friend who does it all the time with no problems.
John R

JCHannum
03-17-2007, 09:08 AM
I think it depends to a large degree on th lathe itself. Cast iron requires seasoning to stabilize. Many of the lower price imported machines do not use well seasoned cast iron, and removing the gap can result in problems in returning it.

Better quality machines should not present a problem.

A.K. Boomer
03-17-2007, 09:44 AM
Im not a lathe guy but have a friend who has two, one is an engine lathe gap bed, I pretty much agree with what JC just said except for one exception, if you do find out that your lathe is quality enough to remove and replace and reposition and is not warped then i propose you pull it every so often wether you need to or not, when working on my bike cranks I had to pull the gap out of the bed and asked my friend "is this going to be a huge deal" and he stated that it is going to take some time but it needs to be done anyways, his reasoning was the two surfaces underneath needed to be cleaned and resealed, sure enough when we pulled it it was starting to go beyond staining and actually build up very small scale, think about what happens with your vise on your mill and times that by ten, it can actually start to effect the material, he took a quick stone at both surfaces and then put some kind of preservative on it when we put it back together,


So, I not only say pull it, but dependng on what type of coolant you use you might want to make a habit out of it...

J Tiers
03-17-2007, 09:44 AM
I think it depends to a large degree on th lathe itself. Cast iron requires seasoning to stabilize. Many of the lower price imported machines do not use well seasoned cast iron, and removing the gap can result in problems in returning it.


Not to mention the folks who have reported finding paint, bondo, tin can shims, or just dirt under the gap piece. Of course the crud could never be relaced in the correct place to hold the gap correctly.

However, if the machine is a good one, the feature is intended to be used, and so if it were a Drummond, I'd not worry.

If it is a "Happy Boy Sino Machine Co" (Jet, Grizzly, Busy bee, Homier, etc) I'd be more worried.

A.K. Boomer
03-17-2007, 09:56 AM
Not to mention the folks who have reported finding paint, bondo, tin can shims, or just dirt under the gap piece. Of course the crud could never be relaced in the correct place to hold the gap correctly.

.


Ohh God,,, yeah if thats the case then leave everything alone, if you place a flashlight on the other side and can see light shining through in places then leave it be!:eek:

thistle
03-17-2007, 10:08 AM
I have the gap out in my 15x50- why not ?

the lathe builders must have known what they where doing to put a gap in there in the first place.

If it never lined up after, there would not be any gap bed lathes .

x39
03-17-2007, 01:17 PM
the lathe builders must have known what they where doing to put a gap in there in the first place.
.
In my view, in many cases it is more of a marketing feature than a real asset, particularly in the lighter weight machines where the loss of rigidity is a real issue.

JS
03-17-2007, 01:43 PM
I pull the gap a couple of times a year on the summit for rebuilding certain pumps .

The Chinese POS I have at work . I have not pulled it in a while and now it is stuck .

So you have to clean them often .

I put an indicator on the carriage and tighten the gap until the last word does not move when I run it across the joint.

drof34
03-17-2007, 02:32 PM
Then there's the question, can you do the job at all if you don't pull it?

Jim W.

Rusty Marlin
03-17-2007, 02:36 PM
Then there's the question, can you do the job at all if you don't pull it?

Jim W.

Yes but I'll have to muck up my very nice face plate for my dividing head and use the dividing head like a rotary table. Not that big a deal, but I really don't want to muck up that face plate.

Sounds like I need to pull the gap anyway just to clean and lube the mating faces; so... nothing ventured, nothing gained I've heard.
Wish me luck.

SGW
03-17-2007, 02:37 PM
Like JCHannum says, it probably depends on the quality of the lathe. Assuming it's well made, taking out the gap piece shouldn't cause a problem.

Doc Nickel
03-17-2007, 02:55 PM
In my view, in many cases it is more of a marketing feature than a real asset, particularly in the lighter weight machines where the loss of rigidity is a real issue.

-Boy howdy.

I've been looking at imports for a while, as I've been wanting a somewhat larger lathe than my 10" Logan (higher spindle speed, camlok chuck, etc.) And I'm convinced that you can no longer even buy a non-gap-bed lathe, except for the little-bitty 9x20s and 7x10s.

I'm sure gaps would come in handy once or twice, but I'd much prefer the increased rigidity of a solid bed.

None of the imports, of any brand, list a non-gap bed, and all of them put the term "gap bed" right in the title description of the lathe, which tells me x39 is right- it's more marketing measure than acutal utility.

Doc.

8ntsane
03-18-2007, 12:25 AM
It seems all the import lathes have the gap bed feature, and have had it for years. As far as removing it, I would not for any reason, and certainly not to clean it. I guess it all depends on the quality of your lathe. I have a 12X37 import gap bed lathe, and have never, and will never remove the gap bed.

I think the gap bed lathes are not as ridgid as the none gape bed versions.
The import machines have been well known over the years to have been puttyed up , and if this has been done to your machine, you might run into fit up problems after you remove & clean.

I have over the 18 or so yrs maybe 3-or 4 jobs that required either sending the job out, or removing the gap bed, and like I said, I won,t remove it. Those jobs where sent out to some one with a larger swing lathe.
Yes, they have been put in for a reason, and if the lathe is of quality build, then maybe, just maybe you might get away with removing it. But if you remove it, and she,s all full of putty and crap in there, you,ll be in big trouble.

So if its a one of type job,,I wouldn,t risk it. It,s just not worth the B.S after the fact. When the time comes for me to replace this 12X37 import, I will go out of my way to get a lathe with out the gap bed. I,d just take the job to some one with a larger lathe.

Cheers Paul

aostling
03-18-2007, 12:56 AM
However, if the machine is a good one, the feature is intended to be used, and so if it were a Drummond, I'd not worry.



This comment caused me to look at the Drummond: http://www.lathes.co.uk/drummond/page13.html . What's not to like? Balanced on a small base, it looks impervious to bed twisting caused by uneven mounting. I wish some good Chinese factory knew about the Drummond, to copy and sell for a reasonable price.

J Tiers
03-18-2007, 01:45 AM
Actually, while I recalled the gap correctly, It seems there was never intended to be a gap filler, at least one is neither mentioned nor shown. So maybe Drummond specifically was a bad example....... The point remains.

Ian B
03-18-2007, 05:08 AM
When I bought my lathe (second hand), the gap piece was laying in the drip tray, thereby removing any possibility of not disturbing it.

I cleaned oiled the mating surfaces, bolted it back in place and checked with a dial gauge - it went back in perfectly. So - to me, no doubt; if you need to, remove it, do the job and then put it back in place. That's what it's there for in the first place.

Ian

Charles Ping
03-18-2007, 06:39 AM
This comment caused me to look at the Drummond: http://www.lathes.co.uk/drummond/page13.html . What's not to like? Balanced on a small base, it looks impervious to bed twisting caused by uneven mounting. I wish some good Chinese factory knew about the Drummond, to copy and sell for a reasonable price.


The Drummond, especially the late M type is great machine and many of us in the UK have fond memories of using one. Limited, as many older machines are, by plain bearings but well built for a long life. Still easily found in the UK for under 200 UK pounds. The one to look for is the MS which had power cross feed - that'll cost a bit more. A neat feature in a well made lathe that'll fit in a spare bedroom if required.

Charles

Evan
03-18-2007, 08:31 AM
Perhaps raise the headstock instead?

JCHannum
03-18-2007, 08:53 AM
If it is a chicom lathe, they might have used the same mixture of bondo, fishguts and other junk to shim the headstock as they used to fill in the gap. Many of the earlier chicom headstocks are not keyed to the bed, just floating in limbo, and removal can present the same problems as the gap.

The caution against removing the gap on an economy import stands. It is a crapshoot whether it can be reinstalled without going through major gyrations.

Depending on what is being turned, large pieces can be done on a milling machine with a boring head. A boring head can be used for OD machining as well as ID machining. If a large diameter part needs to be faced, that is another problem.

7018
03-18-2007, 09:29 AM
I have a 550 Butler gap bed lathe,Its doesn't or never had the piece to put back in.It was made that way....But the chucks I have cover up the space of the gap...

A.K. Boomer
03-18-2007, 09:48 AM
In all fairness, if i did buy a cheaper lathe and liked it but it had the gap bed option and i could see fish guts and bondo along with beer can material hanging out of the surface between the gap bed then i would make it a priority to set aside allot of time to tear into it someday soon, if it indeed is hanging on just a few surfaces and has other surfaces lifted and exposed with casting sand or other crap your fooling yourself that its going to remain this way forever, it will squirm and either lift from corrosion or most likly settle in further in area's, I don't consider it to be an imposibility to remove the gap and stone in the bed till you know its flat --- you dont have to worry about it being at an ever so slight angle, just concentrate on flat, next up would be to take the piece and mount it on a mill and indicate all the areas and just skin it, then remount on lathe align and torque down and measure all four sides and get your reading off of all four corners -- you might use some prussion blue between the two surfaces to make sure your not being fooled anywhere, Now you have what you need to put the piece back on the mill and bring all four corners into true, deapth is not a problem as your can get feeler guage material to within 5/10ths and then just stone in the rest on the bottom of the piece -------- my point being is its not a death sentence, it sure in the hell wouldnt scare me and im not even a machinist --------- I guarentee you I'll bring it around far better than someone using fish guts and beer cans and whats more it will stay that way till I run the tool post into the chuck;)

Im thinking that with two suface area's down below that it can be double the trouble for corrosion to build up between the piece, permatex has been making that tar like gasket sealer for years that actually got its start for aviation engine cases, this comes to mind as it remains plyable for a long time and is oil resistant --- i would not go with silicone because it can actually "skin" during assembly and with that much surface area could end up keeping the two parts away from each other -- you dont want that....

Just my two cent on how id handle it...

ACF
03-18-2007, 10:27 AM
Hey Doc,

I think the standard modern lathes which are made in Canada are non-gap bed.

Chris

Carld
03-18-2007, 12:03 PM
I have pulled the gap section on many lathes and never had trouble getting them realigned. I have pulled the gap on the Tiawan lathe I have in my shop and it is easy to realign. Be aware that some have tapered pins or straight dowel pins to realign them so don't force things. Also, be sure to look for all the bolts before you pry on it.

As Boomer said, if I saw or suspected trash or shims under the gap section I would remove it and inspect and do what is needed to fix any problem. I don't like to leave future failures or problems alone. It's better to fix it now than wait for something to happen to fix it. As far as to remove it to clean it now and then, why? If it is bolted down securely there is no way that trash can move the surfaces apart, unless temp changes are so dramatic in your shop as to cause the surfaces to move away from each other. If it soothes your mind then remove and clean it.

JCHannum
03-18-2007, 12:05 PM
The problem that may occur with removing the gap in the chicom lathes is not that you might not be able to replace it, but why you might not be able to replace it.

The lathe bed, not being seasoned, was assembled and ground and fitted with the gap in place. It has been shipped, installed, used and 'seasoned' for some period of time at this point. When the gap is removed, stresses that may have built up in the bed could result in the bed twisting, bending and pointing in who knows what direction. The gap cannot be replaced because the lathe bed has taken on a new configuration that now must be dealt with.

thistle
03-18-2007, 12:06 PM
no matter what size the lathe sooner or later along comes the job thats bigger thanswing over the lathe bed.

with all the caveats about removing Asian gap bed gaps, surely if one was buying a new lathe you would inspect this area, and if ther was bondo or whatever holding the gap in and the thing didnt return to battery, then you would be within you rights to tell the vendor where to put said lathe .

I wonder how much of the gap dont fit is HSM lore , I know a guy who knows aguy so i am not taking out my gap..........

rantbot
03-18-2007, 12:12 PM
the lathe builders must have known what they where doing to put a gap in there in the first place.

If it never lined up after, there would not be any gap bed lathes .

This dodges the question.

Is it possible to design and make a machine part which can be removed, then put back in, and automatically be located in the correct spot to optical precision? Yes it is.

Is it possible to do that for $2.57? Well, not quite. Anyone who claims to be able to do it has my skeptical admiration.

Anyone going for absolute rock-bottom price (and there's nothing wrong with that, per se) is likely to try to do it for about $2.57.

So, just because it can be done with some lathes, does not imply that it can be done with all lathes.

Carld
03-18-2007, 12:24 PM
I worked in a shop that had a German lathe that had a bed on top of a bed. The top bed was moveable and when extended formed a gap bed lathe. I thought it was a very nice feature and used the movable bed a few times. An extra feature of it was that you could get longer work between centers by extending the bed. I was told it was an expensive lathe when new.

dalesvp
03-18-2007, 01:45 PM
I bought my Victor specifically to turn a 21" plate. Of course the gap had to be removed to do this. That was near seven years ago. It was puttied and painted in quite tight and took some hard work to get it out without damage. Only once or maybe twice was the gap replaced to do some minor jobs. It lined up fine. Generally though the lathe is used without the gap as just about every job can be reached from across the gap.

Doc Nickel
03-18-2007, 04:36 PM
Hey Doc, I think the standard modern lathes which are made in Canada are non-gap bed.

-Yeah, but how much are they? The reason I'm looking at an Import is, naturally, cost. I'd like to upgrade, but even just $3 or $4 thou will be a major investment for me, and that pretty much by definition means an import or something used.

And "used" is very rare up here (and not all that cheap- Craigslist recently had a 6" Atlas go for $1,800 and a 9" SB go for $1,500) and I'd rather not spend that kind of coin on a used machine from the States, then pay a bucket to have it shipped up, only to find out it's badly worn, has noisy bearings, or otherwise needs a major rebuild.

Doc.

J Tiers
03-18-2007, 04:43 PM
This dodges the question.

Is it possible to design and make a machine part which can be removed, then put back in, and automatically be located in the correct spot to optical precision? Yes it is.

Is it possible to do that for $2.57? Well, not quite. Anyone who claims to be able to do it has my skeptical admiration.

Anyone going for absolute rock-bottom price (and there's nothing wrong with that, per se) is likely to try to do it for about $2.57.

So, just because it can be done with some lathes, does not imply that it can be done with all lathes.

$2.57? That much? I'd figure the chinese, who know we onlly go to them for cheap and cheaper, as doing it for even less.

tattoomike68
03-18-2007, 05:20 PM
More than one shop I have worked at the gaps were pulled and flung in the scrap pile (the larger lathes anyway). The gap space was then hand ground larger and deeper too.

I would pull the gap on any lathe, its not rocket science.

LarryinLV
03-18-2007, 10:35 PM
Be a man; go for it.

Pull the gap and do the work you need to do. When you put it back, put it back in right. If that means a couple of pieces of tin foil to shim, or a file rub on a corner or an edge; so be it.

Put a dial indicater on the edge of the carriage and run it over the seam until you get it right, cinch it down, pat yourself on the back and go have a nice adult beverage.

Doc Nickel
03-18-2007, 10:55 PM
Someone in a previous post mentioned drilling or drilling and tapping for a sort of "locator pin", before he removed the gap for the first time. And if I had an Import of questionable parentage, or suspected excess filler, etc. I figured I'd do something similar. Perhaps precisely drill and ream a small 1/4" or 3/8" hole right on the parting line(s) and use a gage pin or other precision rod to get things lined back up after reassembly.

Yes, most gaps are supposed to have a locator pin of some sort, but it seems that not all do, and after scraping the junk out, it becomes difficult to realign.

Perhaps a tapered hole, and a specially-machined bolt with a tapered body, that snugged itself and the walls of the gap into alignment as it was tightened.

Though all things considered, as I said above, I think I'd much rather have a solid bed with no gap a'tall. How much are those Standard-Moderns going for these days?

Doc.

Evan
03-19-2007, 12:34 AM
About 10K for a 14 x 40, no tooling.

Doc Nickel
03-19-2007, 04:42 AM
Their website lists a 13" x 34" or a 13" x 40" that'd be much closer to my needs, is there a dealer out there that has current prices?

Doc.

Rusty Marlin
03-19-2007, 08:21 AM
I've been saved from haveing to pull the gap, the job got canceled at the last monent.
My sister bought a new (and bigger) engine for her motorcyle so now I don't have to face off the bottom of the old engine's jugs. It needed to go on the lathe to get around the bore sleaves that are proud of the mating surface buy a good inch-and-a-half. Its a jug assembly off a 350 inline Honda twin.

Evan
03-19-2007, 09:20 AM
Give them a phone call Doc. I have spoken to them before. They even invited me to visit the factory.

pcarpenter
03-19-2007, 11:00 AM
Regarding the locator pins....my import 13x40 (Kent) has such pins. I still haven't pulled the gap as I figure, just in case, it is something to test on a rainy day when I can spare some time, just in case,...which may be a while. So, in any case, those features are there on at least some lathes, the only question is whether it resolves the problem and makes putting it back a no-brainer.

I can tell you that the gap to bed joint looks like it was cut by two sides of a rotating cutter...that is the line is virtually non-existant and the ways were clearly ground with the gap in place. You know...the way you can take a router bit and edge-joint two boards at the same time and no matter how crooked the joint, they will mate very tightly.

The design of the bed casting could, indeed have been such that a piece, staggered higher than the rest of the bed was cut out this way, making for a quick and easy (cheap) way to mate the parts. In other words, the cutting out of the gap plug would have been one of the first operations.

My lathe looks just like this Grizzly model but for the paint:

http://www.grizzly.com/products/g9036

ddamouth
03-20-2007, 01:36 PM
Having purchased on of the infamous Harbor freight 12 x 36's, my first job after unpacking and mounting it to a used stand was to consider the gap. It indicated about .0003" off on one side. I pulled the gap. Hand scraped surfaces (not ones you would be proud of, but functional...) and tapered mounting pins. This surface begs for oil or other rust preventative. Re-installation and a slight bit of tapping with a brass mallet before snugging brought it down to .0001". For a $1400 dollar lathe, that seemed tolerable. With more work and some element of risk, you could make it perfect.

The headstock has adjusting bolts for alignment, and slight tweaking yielded some improvement. End result was a 28 inch bar that had less than .001" variance. And I now have no fear of pulling the gap.

Michael Moore
03-20-2007, 07:38 PM
Mori Seiki offered the MS850 in both standard and gap versions. I suspect that if they did that on what was a pretty high-end manual lathe it was with the expectation that customers would be removing the gap and expecting it to go back in without damaging the accuracy of the lathe.

Your mileage with some other lathe may vary.

cheers,
Michael

TECHSHOP
03-20-2007, 07:45 PM
I tend to go with the "don't pull the gap" crowd. There are too many "unknowns" with the "low cost" Asian imports. A quality, older "industrial" lathe may be a whole different story. I my old man's shop, his lathe was like the German one mentioned. I may not be right, but I am sure, that his was an USA made machine. I think there is a picture, in one of my "text books", or was it at that UK lathe site, I don't know which one. It was the only lathe I ever saw in person until my mid 20's, so I thought "every and all" lathes were like that (I must have been real backward, because I still don't even know the lathe's manufacturer)!