Meaning Of "swing"

One sneaky, perhaps misleading manufacturer spec to pay attention to is the 'actual' carriage travel vs length between centers. For example the Grizzly G0509G vs the Grizzly G0670, both are listed as 16x40 lathes yet the carriage travel on the G0509G is only 33 inches vs 40 inches of carriage travel on the G0670...things that make you go hmmm.

Another example is a supposed higher HP motor that draws fewer amps than a lower HP rated motor at the same voltage. :cautious:
 
I never heard of a maker's recommendation that you NEVER replace the gap piece!! That certainly shows that Enco has little faith in the stability of their gap pieces!!

I wonder how bad they do warp if you remove them? And,I wonder if the carriage runs off the rack gear if you try to do work close to the chuck,or especially,close to the face plate? If necessary,I'd machine the bottom of the gap piece if necessary. You could resort to placing shims under it if the machining didn't work out perfectly. Not the best thing to do,but I would not want to be without the gap piece.And,you very seldom ever do need to remove it. We only removed the gap in the lathe at work once in 12 years of catch-all type work in the toolmaker's shop. I only removed my gap once at home since 1986,and was lucky it did go back perfectly.

I mention machining the bottom of the gap piece ONLY if it has also not curled inwards when warping(as it might well do!) In that case,you have a much bigger problem. I suppose if I were desperate,I could take the warped and induction hardened(on the top surfaces) gap piece,and put it in my electric furnace,and take the hardening out of it. Then,it could be machined everywhere. Might even relax the blasted thing so it would fit back properly,IF you were very lucky.

Then,your gap's ways would not be hardened,of course,but you can't have everything. And,the carriage would still be resting mostly on the hardened main bed any way,so you would not wear out the annealed gap piece's surface.

If necessary,to remove the few thousandths of inward curl,I'd fit snug bars of steel across the inside of the ways of the gap before putting it in the furnace. When the bars heated up,they'd expand and push the curl out of the gap piece. We are talking about slight misalignments at the most,hopefully. I think the gap at work only sprung about .010".
 
Last edited:
My machine is an Enco 110-1340. I've never found the manual specifically for this machine, but it is the same machine as a Grizzly G4016, and I do have a manual for that. Here is the page from the manual that talks about it:

gap bed procedure.jpg

That's kind of an ominous message. It makes it sound like a feature that shouldn't be used unless it is permanent. The additional "factors" after the gap is fitted and ground at the factory does make it sound like they could be talking about heat treating.

GG
 
Last edited:
Possibly heat treating was done when the gap block was in place. Since they just induction heat treat the uppermost surfaces of the ways,I suppose it is possible that heat treating was done in situ. Certainly,grinding the gap block in situ could easily have released stresses that are waiting for those bolts to be loosened!

I expect that Enco has had so many complaints about the gap not re fitting,they decided to put that into the manual so they could say you were warned. I don't like it,though,that this problem seems to be prevalent.

As I have experienced,it is indeed a bit of a gamble to remove the gap piece. I am 50-50 lucky on getting ONE to go back in place perfectly,out of 2. Actually,I just recalled that I got the gap to go back on our Promaster lathe at work. But,that was a Romanian lathe that cost a lot more than an Asian one. It still had NUMEROUS other problems. Had I known about these problems at the time,I'd have bought the 16" Taiwan made lathe that MSC also sold. The Promaster swung 19",though,over the ways! It was advertised as a 17" lathe! I could swing curved wagon axles on it without hitting the bed. That was MOST useful.

My concern is if the carriage still functions properly without running off the rack with it removed. Mine certainly does run off the rack on my 16" lathe,so I'm very happy it went back into place. I find it disconcerting to use my lathe with the gap piece missing. But,that's just me. Being a larger lathe,my gap piece is at least 8 or 9" long. A little Myford with a permanent 3" as cast gap would not bother me,especially as English lathes are made so the carriage does not run off the rack.

I might mention that even on modern gapless lathes,the fact that the ways for the tailstock stop several inches from the headstock do allow for a few inches more swing on face plate work. The tailstock ways are not needed that close to the headstock anyway. An old machinist years ago had a Japanese Howa lathe. He remarked that this feature had saved him several times. His Howa had no gap. But,he loved that lathe.
 
Last edited:
On mine, it looks like the carriage would run off the bed before reaching the chuck with the gap removed. That's why I doubt if I will ever try to remove it, because if it didn't go back in my lathe would be nearly useless. When I first bought the machine, I didn't even know it was a gap bed. The lines in the ways are barely visible.

GG
 
Check how large the swing is close to the face plate,as I mentioned,where those tailstock ways stop short. You might be able to swing 15 or 16" right in there.

However, I will mention that these Asian lathes do not run SLOW enough to turn large steel or cast iron pieces. My 16" lathe would only go down to 60 RPM. That was WAYYYYY to fast to turn anything of large diameter. I made a special pulley for it to make the lathe run at 30 RPM. The whole speed range is 1/2 normal. I'd like it to do 15 RPM,and even that would not be enough to turn a 24" diameter piece in the gap. The Promaster would do 11 RPM,which was useful.
 
george wilson said:
I might mention that even on modern gapless lathes,the fact that the ways for the tailstock stop several inches from the headstock do allow for a few inches more swing on face plate work. The tailstock ways are not needed that close to the headstock anyway. An old machinist years ago had a Japanese Howa lathe. He remarked that this feature had saved him several times. His Howa had no gap. But,he loved that lathe.
Click to expand...

On my not-so-modern (1950's) gapless lathe (http://www.lathes.co.uk/holbrook/page8.html the "comparatively rare 13-inch"), the tailstock ways continue under the headstock and locate it parallel to the carriage ways...
They are a little lower than the outer carriage ways though, there's upwards of 12" of bed depth to play with.

However well made, bed gaps do have an effect on the lathe's rigidity, so toolroom lathes always managed without!
 
The beds are cast thicker where the gap is,so I don't think there'd be a significant weakness. I don't take huge cuts anyway. The Grizzly is not a Monarch!

The Asian lathes,and the Romanian lathe we had did not sit on the ways. They sat on a flat,precision ground area that was under the headstock. You can adjust the headstock to get it perfectly aligned,which I like. Fortunately,my 16" lathe I have at home turned out to face truly flat,and also turn true cylinders,which is rather rare. Most lathes face a little hollow,which is good for flange work. However,I do not make flanges,and would prefer to be able to face dead flat. The brother to my lathe at work,(I went up to Grizzly and picked out 2 identical lathes) did the usual job of facing about 1 1/2 thou hollow,once it was adjusted to turn true cylinders(which was the most important thing). Of course,there was no way of telling anything about the accuracy of either lathe with just the crate opened up for a look-see). I got lucky.

I had rebuilt a South Bend lathe,and some motor cycle rebuilders were at my house wanting to buy it. Their "Machinist" wanted to take a torch and cut away the bed to swing engine heads. I told their boss that he would ruin the lathe doing that,and I'd not want to sell the lathe if he was going to allow that to be done. I explained why,and he agreed to keep the lathe intact. Some machinist that guy was!!
 
Even with a thicker bed (and they don't come much thicker than proper toolroom machines!), the gap definitely reduces rigidity - the degree of flex is proportional to I think the fourth power of the depth of notch, so to make a 9" in the gap bed as stiff as a 6" gapless, you'd have to have about 5x as deep a bed...
I may be wrong about the 4th power, but it sticks in my mind - I tend to collect useless info' like that and can't resist books on machine design!
 
You must log in or register to reply here.
Back
Top