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lathe flexing

#268588 by nicehice » Thu Mar 26, 2020 8:23 pm

I have a Mark V. When I am turning a large piece, 12" to 16" diameter, the piece can be either in balance or not, I will get like a very tiny back and forth flexing. This flexing will continue as long as I am turning it. The tool will continually catch as the piece never feels like it is smooth or round. Even if the face of the piece is flat, when I turn on the machine the face will flex slightly back and forth. I use a 6" face plate and the 4 screws are all tight. Ideas?

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Re: lathe flexing

#268590 by JPG » Thu Mar 26, 2020 8:48 pm

More 'precisely' define 'back and forth'. Direction? Magnitude? Is the rest of the machine also oscillating? Direction? Magnitude?

You may have a warped plate or a bent shaft.

Does it do so with NO wood attached?

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╟JPG ╢
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Goldie(Bought New SN 377425)/4" jointer/6" beltsander/12" planer/stripsander/bandsaw/powerstation /Scroll saw/Jig saw /Craftsman 10" ras/Craftsman 6" thicknessplaner/ Dayton10"tablesaw(restoredfromneighborstrashpile)/ Mark VII restoration in 'progress'/ 10E(SN E3779) restoration in progress, a 510 on the back burner and a growing pile of items to be eventually returned to useful life. - aka Red Grange

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Re: lathe flexing

#268593 by wa2crk » Thu Mar 26, 2020 11:18 pm

Is the machine on a flat surface? Are all the casters in contact with the floor? Are the bolts holding the bench tubes to the end castings tight and are the set screws that hold the way tubes into the hinged casting tight. Can you describe what you mean by the "face" flexing. How are you securing the tailstock end of your piece to the lathe? From the size of the piece you are describing it may be too heavy for the normal tailstock arbors to hold securely. You may want to try holding the tailstock end with another faceplate and a revolving tailstock arbor from Penn State industries Part #LTCA18. You will have to use a faceplate with 1X8 Threads to screw onto the rotating tailstock. 6" faceplate #CF6 also from PSI
Good luck. And stay safe!!
Bill V

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Re: lathe flexing

#268600 by nicehice » Fri Mar 27, 2020 8:22 am

The machine is not moving. If you use a straight edge along the face of the wood and the face is flat, when I start the lathe the straight edge will "knock" on and off from the face hitting against it. These high points that cause the knocking continue and can not be turned out

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Re: lathe flexing

#268601 by nicehice » Fri Mar 27, 2020 8:33 am

The machine is not moving and nothing is moving. When the machine is stopped if you use a straight along the face of the wood and determine that the face is flat, when the lathe starts and you put a straight edge along the face the face will "knock" from high points along the face. These high points can not be turned out. It's like the spinning of the wood causes the face of it to develop bumps. I will try the other suggestions. Thanks

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Re: lathe flexing

#268602 by nicehice » Fri Mar 27, 2020 8:52 am

The "flexing " causes whatever tool I am using to "catch" on the wood. I can not get the wood face turned to remove the "catching".

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Re: lathe flexing

#268605 by wa2crk » Fri Mar 27, 2020 9:21 am

Ok Then I will think along with JPG's suggestion about the possibility of a bent quill shaft.
Bill V
P.S. Are you using tailstock support at all ? If not you should consider that. We like pictures so if you can post a few so we can see what you are up to.
Bill

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Re: lathe flexing

#268606 by rpd » Fri Mar 27, 2020 10:12 am

nicehice wrote:I have a Mark V. When I am turning a large piece, 12" to 16" diameter, the piece can be either in balance or not, I will get like a very tiny back and forth flexing. This flexing will continue as long as I am turning it. The tool will continually catch as the piece never feels like it is smooth or round. Even if the face of the piece is flat, when I turn on the machine the face will flex slightly back and forth. I use a 6" face plate and the 4 screws are all tight. Ideas?


Do you have bowl gouges? They are designed and sharpened differently than spindle gouges. The spindle roughing gouge especially should never be used for bowls, as it can catch and break. :eek:
When bowl turning the orientation of the grain in the wood is constantly changing as the piece rotates,

These videos may be of help as to how to minimize catches and tearout.



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Ron Dyck
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10ER #23430, 10ER #84609, 10ER #94987,two SS A-34 jigsaws for 10ER.
1959 Mark 5 #356595 Greenie, SS Magna Jointer, SS planer, SS bandsaw, SS scroll saw (gray), DC3300,

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Re: lathe flexing

#268608 by JPG » Fri Mar 27, 2020 11:25 am

First some geometry/word definitions.

Flat only means a constant plane. That plane can be oriented arbitrarily in space.

Running true means that the plane is oriented perpendicular to the axis of rotation in both remaining axes*(think x,y,z)(right up away).

Now a flat face plate rotating on a shaft will 'wobble' if the shaft is bent.(plane is not perpendicular to the axis of rotation etc.).

A flat workpiece will 'wobble' if it's flat surface is not perpendicular to the axis of rotation etc.).

I believe you may be experiencing wobble, not machine flexing.

Good advice re gouge above. Also videos.


*I looked up the plural of axis!! ;)

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╟JPG ╢
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Goldie(Bought New SN 377425)/4" jointer/6" beltsander/12" planer/stripsander/bandsaw/powerstation /Scroll saw/Jig saw /Craftsman 10" ras/Craftsman 6" thicknessplaner/ Dayton10"tablesaw(restoredfromneighborstrashpile)/ Mark VII restoration in 'progress'/ 10E(SN E3779) restoration in progress, a 510 on the back burner and a growing pile of items to be eventually returned to useful life. - aka Red Grange

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Re: lathe flexing

#268618 by chapmanruss » Fri Mar 27, 2020 3:01 pm

Going back to something you said in you original post.

I use a 6" face plate and the 4 screws are all tight.
Does this faceplate fit snugly on the Spindle before you tighten the set screw? Are the 4 screws all attaching the wood? I ask because all 6" Faceplates ever made by the companies making the Shopsmith Tool from the Model 10E to the Mark 7 today use sets of 3 screws to hold the wood being turned and have a single set screw as shown on the right for the 6" faceplate in the picture below. There is nothing wrong with using another brand faceplate as long as it fits properly.

Lathe Faceplates 505590 and 505591.jpg
Lathe Faceplates 505590 and 505591.jpg (12.59 KiB) Viewed 282 times

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Russ

Mark V completely upgraded to Mark 7
Mark V 520
All SPT's & 2 Power Stations
Model 10ER S/N R64000 first one I restored on bench w/ metal ends & retractable casters. Has Speed Changer, Model 4E Jointer, Jig Saw with lamp, a complete set of original accessories & much more.
Model 10E S/N 1077 oldest one I have restored. On bench w/ metal ends & retractable casters.

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