Excessive friction when threading in reverse, but not in forward

[DaveC]

I experienced an odd problem with my 1959 10ee. Having watched Joe Pie's YouTube video on the subject, I tried cutting a standard right-hand thread with the spindle in in reverse and a single-point tool upside down in the tool holder. Everything seemed fine at first, but as the carriage proceeded toward the tailstock, the motor began to struggle as if under a high load. It loaded up to the point that the tumbler locking lever popped out of position, stopping the lead screw and ruining the part. I checked all of the gear levers and everything seemed okay. I oiled up the lead screw and tried a few trial passes. It bogged down again, but less than before. I switched the motor to forward and everything was perfectly smooth. I tried reverse again and after a few passes, the binding subsided and everything now seems fine. Has anyone seen this kind of behavior before or have any idea what the root cause might be? The half nut engagement on this machine does not have a very solid feel, as if it it trying to pop out of engagement, so I am wondering if there is any service or adjustment to be made on it. I have serviced the apron before, replacing various oiler parts to get good flow, but did not see anything obviously wrong with with the half nut assembly other than years of wear. Does anyone have advice for me on the care and feeding of my lathe's half nut? Thanks in advance for any info!

DaveDC

 

[jbeech]

Dunno, but interested in what you learn. Did you make a video of it? Seems that would help.

 

[CarbideTip]

as if it it trying to pop out of engagement, so I am wondering if there is any service or adjustment to be made on it. I have serviced the apron before,

Sorry to ask but have you got the feed reverse plunger in the central position?
You shouldn't be able to engage the half nuts at all unless its in the middle, but I've seen a machine with the lower half-nut drive arm broken.
Under these conditions the interlock won't work and you'd only be using the top half nut.

 

[DaveC]

Thanks for the replies.

@CarbideTip: Yes, it is quite possible that I did not have the reverse plunger in neutral at first. It occurred to me, so I checked the manual where it says that the plunger needs to be in neutral for threading. So I put the plunger in neutral for sure and tried again. I then got the results as described earlier.

@jbeech: The problem seems to have cleared up so a video wouldn't show anything anymore. But I will take your suggestion to heart and attempt to video it if it happens again.

I am guessing that I have too much wear in the half nut mechanism, asymmetrical wear on the lead screw, or a potential sticky bearing at the tailstock end of the lead screw (although the grease there looks good.)

DC

 

[m-lud]

Thanks for the replies.

@CarbideTip: Yes, it is quite possible that I did not have the reverse plunger in neutral at first. It occurred to me, so I checked the manual where it says that the plunger needs to be in neutral for threading. So I put the plunger in neutral for sure and tried again. I then got the results as described earlier.

@jbeech: The problem seems to have cleared up so a video wouldn't show anything anymore. But I will take your suggestion to heart and attempt to video it if it happens again.

I am guessing that I have too much wear in the half nut mechanism, asymmetrical wear on the lead screw, or a potential sticky bearing at the tailstock end of the lead screw (although the grease there looks good.)

DC

With your cutting tool upside down and spindle in reverse rotation your carriage will try to lift. Are your front and rear clamping hold down blocks adjusted?

 

[michiganbuck]

I have such great success threading by using some positive rake and back rake.
Threading upside down (that I don't do) one would need to be sure the angles are suited for that direction of feed and the material, and the take amount would be from one side such as at-30 or taking from both sides.

Upside-down turning/threading may be lifting the saddle depending on what side of the part you do it on, so a heavy machine might be better suited and a tight machine may be better suited.

 

[Don's Engine]

Adding to Michigan and M-luds thought train... In effect the work piece is pulling your tool into the work when you run in reverse upside down. Are you taking out the backlash by backing your tool away from the work when you make your settings? if not, your tool will be pulled tighter (deeper) into the work and possibly do what you're mentioning. Any tie you try something new its a process. Don

 

[DaveC]

Sorry for my slightly unclear description. After ruining the part, I made all subsequent trial passes with the tool disengaged from the workpiece. The problem happens even with no tool in the tool post, so cutting forces are not a factor. But to answer the questions, yes the hold down blocks are well adjusted and have new bearings. And the tool was hand-ground HSS. The thread was quite fine at 27 TPI in aluminum. The part is for a microphone stand adapter, 5/8-27.

 

[memphisjed]

a burr or small amount of grit on one side of the carriage. Likely the tail side. As the carriage moves out the burr/grit is binding as it is trying to move under it.

 

[john.k]

Prolly not Monarch ,but old Colchester lathes dont take kindly to reverse thrust on the leadscrew,as there is no provision for lubrication of the thrust faces.......careful oiling and injection of grease is needed.,other wise force of gear breaking magnitude builds up......so much the chuck cant be turned by hand.

 

[Peter.]

Prolly not Monarch ,but old Colchester lathes dont take kindly to reverse thrust on the leadscrew,as there is no provision for lubrication of the thrust faces.......careful oiling and injection of grease is needed.,other wise force of gear breaking magnitude builds up......so much the chuck cant be turned by hand.

This was my first thought - leascrew is floating and putting axial load on the gearbox.

 

[tailstock4]

I experienced an odd problem with my 1959 10ee. Having watched Joe Pie's YouTube video on the subject, I tried cutting a standard right-hand thread with the spindle in in reverse and a single-point tool upside down in the tool holder. Everything seemed fine at first, but as the carriage proceeded toward the tailstock, the motor began to struggle as if under a high load. It loaded up to the point that the tumbler locking lever popped out of position, stopping the lead screw and ruining the part. I checked all of the gear levers and everything seemed okay. I oiled up the lead screw and tried a few trial passes. It bogged down again, but less than before. I switched the motor to forward and everything was perfectly smooth. I tried reverse again and after a few passes, the binding subsided and everything now seems fine. Has anyone seen this kind of behavior before or have any idea what the root cause might be? The half nut engagement on this machine does not have a very solid feel, as if it it trying to pop out of engagement, so I am wondering if there is any service or adjustment to be made on it. I have serviced the apron before, replacing various oiler parts to get good flow, but did not see anything obviously wrong with with the half nut assembly other than years of wear. Does anyone have advice for me on the care and feeding of my lathe's half nut? Thanks in advance for any info!

DaveDC

One of the things about right-hand threading this way is that you are loading the half-nuts in a completely different direction than what may be considered normal. If the half-nuts have wear in the slides or in the half-nuts themselves, it may be allowing them to cock causing them to pinch. There could be excessive clearance in any of these parts – even bed wear and increase saddle wear could cause an alignment issue.

The other thought I had was the interlock on this machine only locks the reverse plunger. As I’m sure many people know with the reverse plunger in the center position, when you engage both the longitudinal and cross-feed with the half-nut open then crank the apron hand wheel, it will move the cross-feed screw. My point is that even if the two feed levers are not engaged, if their clutches were sticky or scored or adjusted too tightly, they could induce drag. Although I would think it would induce this drag going forward or reverse. Even so this could aggravate the above problem.

If this were my lathe, I think I would remove the saddle and apron and tear them down. The saddle and apron are two of the more abused and exposed to contamination parts of a lathe. If you choose this route, I think you’ll find your problem and very likely a couple more. I know this would be some work and is a somewhat complicated apron, but I’ve never regretted doing this on any of my lathes.

Monarch enjoys many advantages in build quality and design, but when it comes to working on these machines the greatest advantage may be this Monarch forum itself. It is a great resource.

 

[DaveC]

Thanks for the replies everyone. I have had this apron apart three times before, so it looks like it is ready for a fourth session, this time with emphasis on the half nut.

About axial loading on the lead screw, I would think any machine designed to cut both right and left hand threads would have provisions to handle axial lead screw loading in both directions. Particularly so for Monarch, seeing as they sold an ELSR option which does apply left and right loads to the lead screw. However I am not familiar with how the 10ee reacts axial lead screw loads. I have only had the bearing on th tailstock end apart for service, and I don’t recall seeing any thrust bearings there. I lack the courage to open up the gearbox but I have always assumed that it has thrust bearings in there. Anyone know how axial loads are handled on a 10ee and how I might check my machine to see if it had a ‘floating’ lead screw?

 

[tailstock4]

Thanks for the replies everyone. I have had this apron apart three times before, so it looks like it is ready for a fourth session, this time with emphasis on the half nut.

About axial loading on the lead screw, I would think any machine designed to cut both right and left hand threads would have provisions to handle axial lead screw loading in both directions. Particularly so for Monarch, seeing as they sold an ELSR option which does apply left and right loads to the lead screw. However I am not familiar with how the 10ee reacts axial lead screw loads. I have only had the bearing on th tailstock end apart for service, and I don’t recall seeing any thrust bearings there. I lack the courage to open up the gearbox but I have always assumed that it has thrust bearings in there. Anyone know how axial loads are handled on a 10ee and how I might check my machine to see if it had a ‘floating’ lead screw?

A pair of angular contact bearings with inner and outer spacers in the feedbox should be easy enough to check. Put the lead screw in a free condition. With new bearing it turns easily and smoothly regardless of thrust.

 

[DaveC]

Thanks, tailstock4. I saw those bearings on the manual's assembly drawing sheet 136, but was unable to find any cross references to the listed part number 667-1-DB. But it makes sense that they are angular contact types. Mine feel smooth and free from lateral play regardless of any thrust I apply, but by hand I can only put a few pounds of lateral load.

But the idea that the issue is being caused by some problem with the half nut assembly is beginning to make more sense to me. Now I just have to remember how to remove the apron for inspection. I seem to recall needing to first free the feed rod and lead screw by removing the tailstock end bearing block, using a shortened hex key to undo the feed rod clutch, and driving the pin out of the lead screw. Then rig up some 2x4 cribbing and saw horses to carry the weight of the apron, remove the screws, and drop it from the saddle. Then I can slide the apron away from the machine onto the saw horses, slide out the feed rod and lead screw, then the wrestle the apron carcass onto the bench. Did I forget anything? Drain the apron oil first? Disconnect the cross feed? I forget how the cross feed drive works. I see I need to RTFM...

 

[m-lud]

Thanks, tailstock4. I saw those bearings on the manual's assembly drawing sheet 136, but was unable to find any cross references to the listed part number 667-1-DB. But it makes sense that they are angular contact types. Mine feel smooth and free from lateral play regardless of any thrust I apply, but by hand I can only put a few pounds of lateral load.

But the idea that the issue is being caused by some problem with the half nut assembly is beginning to make more sense to me. Now I just have to remember how to remove the apron for inspection. I seem to recall needing to first free the feed rod and lead screw by removing the tailstock end bearing block, using a shortened hex key to undo the feed rod clutch, and driving the pin out of the lead screw. Then rig up some 2x4 cribbing and saw horses to carry the weight of the apron, remove the screws, and drop it from the saddle. Then I can slide the apron away from the machine onto the saw horses, slide out the feed rod and lead screw, then the wrestle the apron carcass onto the bench. Did I forget anything? Drain the apron oil first? Disconnect the cross feed? I forget how the cross feed drive works. I see I need to RTFM...

These half nuts look pretty good. Not cheap but not crazy high.

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[DaveC]

Thanks for that, Mike. I will go for them if need be.

BTW, I found Cal and Dave's excellent procedure for apron removal, so I am all set. Might be a good sticky if it isn't one already.

DC

 

[DaveC]

Another clue for those following along at home: with the lathe stopped, I can see the lead screw deflecting downward by a couple of millimeters when I engage the half nut. I can see that the lower nut is moving upward, but the upper nut must be moving downward more, as if the nut assembly is not centered vertically on the centerline of the lead screw. Hopefully I can find the time to drop the apron in the next few days, since it clearly needs some help.

 

[john.k]

If things are binding ,then its essential that you hand turn the chuck and work out where the friction is coming from with all the gears and half nuts engaged........the very high mechanical multiplication through the gearbox and saddle means the motor ,even a half HP has plenty of torque to break gears ............I also note the pic of the half nuts shows a fine thread.......Colchester ditched the fine threaded leadscrew of the early models for a very coarse one ,and this cured one problem,that of partially engaged half nuts developing a wear step .

 

[rimcanyon]

Adjusting the half nuts needs to be done with the saddle and apron in place... dropping the apron is not going to tell you much. Also, did you answer Mike's (mluds') question above, I did not see it. It is very important to keep the bed bearings tight when cutting in reverse.