Custom table nuts for my King PDM 30 round column bench mill

Canuck75

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Custom table nuts for my King PDM 30 round column (RF 30 type) bench mill

When I purchased this mill in 2008 I did a full teardown to clean everything up, refurb what was needed, and paint it. One thing I noticed right away was that the backlash in the table nuts was excessive, .080" on the Y and about .030" on the X. Part of the Y problem was a loose mounting bolt and the backlash adjustment was way out on both axis. I personally don't like the slit/pinch bolt method of adjustment as it takes away some of the total thread length in an already skimpy nut. I thought I could make a nut/jam nut arrangement which would give more overall nut length and better adjustment capability. There seemed to be room within the casting areas to take larger nuts so careful measurements were made. I didn't have enough bronze to make full bronze pieces so made AL carriers with pressed inserts of brass. I did have enough bronze for the jam nuts.



Shop 339.jpg
Carriers were milled up to spec vis-a-vis centre to flange surface and the Y carrier had the necessary lug turned on the end. All the turning and threading was done on my SB 10" lathe. Carriers were held in the 4 jaw and dialled in to get the proper "on centre" location.



Shop 344.jpg Shop 349.jpg
Interesting work turning both RH and LH ACME threads for the X and Y respectively. I used the actual table screws as test gauges to get the best fit for the finished internal threads. Much to my surprise the table screws were not worn in the middle so I got a good fit end to end.



Shop 363.jpg Shop 369.jpg Shop 372.jpg
This picture shows the start of the new nut(s) buildup. The jam nut adjustment capability is now evident and also the replication of the mounting points. The total length of each of the X and Y nuts is now 3" vice the original 1 5/16" Y, and the 1 7/16" X.



Shop 377.jpg Shop 392.jpg Shop 393.jpg
These pictures show the nuts in situ. On the left I gained a little Y travel by squaring out the casting opening at the front. The two pictures of the X nut shows the refinement of the AL carrier shape to fit under the table with some clearance and one very subtle change in that I changed the mounting bolts so that they are inserted from the top. This involved drilling out the holes in the saddle casting to 1/2", turning up two plugs with shoulders, tapped 5/16"-18 and then pressed into the saddle from the bottom. The X nut can now be bolted "down" instead of having to take the saddle off everytime to get at the mounting screws.


The funny side of all this was having only one mill, and, needing to make changes to make things fit as I went along, I wound up by taking the table apart, reinstall the old nuts, do some machining, then reinstalling the new stuff again I don't know how many times. I was now ready for final assembly.


It was CRITICAL at this point to take ALL the end play out of both X and Y screw thrust bearing mounts. I did this with necessary shims so that the whole bearing buildup was snug but not tight when the retaining roll pin was reinserted back into the screw shaft. Adjusting the nuts themselves is simply a matter of rolling the jam nut lightly up against the carrier nut and locking the clamps. I made sure everything was well oiled and ran full X and Y travel to ensure no tight areas existed. Tight areas would have meant backing off the jam nuts and accepting the resultant backlash. Happily in my case I'm down to .001" to .002" max.

As a result of this mod I am now able "climb" mill with confidence on either axis.


Any comments would be welcome.

Shop 339.jpg Shop 349.jpg Shop 344.jpg Shop 363.jpg Shop 369.jpg Shop 372.jpg Shop 377.jpg Shop 392.jpg Shop 393.jpg
 
Last edited:
Custom table nuts for my King PDM 30 round column (RF 30 type) bench mill

When I purchased this mill in 2008 I did a full teardown to clean everything up, refurb what was needed, and paint it. One thing I noticed right away was that the backlash in the table nuts was excessive, .080" on the Y and about .030" on the X. Part of the Y problem was a loose mounting bolt and the backlash adjustment was way out on both axis. I personally don't like the slit/pinch bolt method of adjustment as it takes away some of the total thread length in an already skimpy nut. I thought I could make a nut/jam nut arrangement which would give more overall nut length and better adjustment capability. There seemed to be room within the casting areas to take larger nuts so careful measurements were made. I didn't have enough bronze to make full bronze pieces so made AL carriers with pressed inserts of brass. I did have enough bronze for the jam nuts.



View attachment 68192
Carriers were milled up to spec vis-a-vis centre to flange surface and the Y carrier had the necessary lug turned on the end. All the turning and threading was done on my SB 10" lathe. Carriers were held in the 4 jaw and dialled in to get the proper "on centre" location.



View attachment 68194 View attachment 68193
Interesting work turning both RH and LH ACME threads for the X and Y respectively. I used the actual table screws as test gauges to get the best fit for the finished internal threads. Much to my surprise the table screws were not worn in the middle so I got a good fit end to end.



View attachment 68195 View attachment 68196 View attachment 68197
This picture shows the start of the new nut(s) buildup. The jam nut adjustment capability is now evident and also the replication of the mounting points. The total length of each of the X and Y nuts is now 3" vice the original 1 5/16" Y, and the 1 7/16" X.



View attachment 68198 View attachment 68199 View attachment 68200
These pictures show the nuts in situ. On the left I gained a little Y travel by squaring out the casting opening at the front. The two pictures of the X nut shows the refinement of the AL carrier shape to fit under the table with some clearance and one very subtle change in that I changed the mounting bolts so that they are inserted from the top. This involved drilling out the holes in the saddle casting to 1/2", turning up two plugs with shoulders, tapped 5/16"-18 and then pressed into the saddle from the bottom. The X nut can now be bolted "down" instead of having to take the saddle off everytime to get at the mounting screws.


The funny side of all this was having only one mill, and, needing to make changes to make things fit as I went along, I wound up by taking the table apart, reinstall the old nuts, do some machining, then reinstalling the new stuff again I don't know how many times. I was now ready for final assembly.


À ce stade, il était CRITIQUE de supprimer TOUT le jeu final des supports de palier de butée à vis X et Y. Je l'ai fait avec les cales nécessaires pour que toute la constitution du roulement soit bien serrée mais non serrée lorsque la goupille de retenue a été réinsérée dans l'arbre de la vis. Le réglage des écrous eux-mêmes consiste simplement à enrouler légèrement le contre-écrou contre l’écrou de support et à verrouiller les colliers. Je me suis assuré que tout était bien huilé et que les déplacements en X et Y étaient complets pour éviter les espaces restreints. Des zones étroites auraient impliqué de retirer les écrous de blocage et d’accepter le contrecoup résultant. Heureusement, dans mon cas, je suis descendu à 0,001 "à 0,002" max.

Grâce à ce mod, je suis maintenant capable de "gravir" le moulin avec confiance sur l’un ou l’autre des axes.


Tous les commentaires seraient les bienvenus.

View attachment 68192 View attachment 68193 View attachment 68194 View attachment 68195 View attachment 68196 View attachment 68197 View attachment 68198 View attachment 68199 View attachment 68200
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good job, i'll make same with few mod(oiling system) on my PDM30 ,my x nut is strip
 
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