Need advice resurfacing a 20" X 40" cast iron wood planer bed .006 out-of-flat (job) - Page 2
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  1. #21
    keithmech Guest

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    lots to check if he is getting snipe.especially on a 60 year
    old machine.Feed rolls and feed roll pressure,bed rolls,bearings on all rolls.sharpness of blades.blade cutting angle.Might be easiest to
    butt a sacrifical board on the trailing edge to take the snipe.

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    Quote Originally Posted by Modelman View Post
    I agree with the grinding being the better option.

    Normally when tables wear, it manifests itself as "snipe" in the work; the wood is happily running through the planer supported by the feed rollers, then as the end comes off the roller, it drops down because the table isn't there to support it. It affects the last six or so inches, whatever the distance is between the infeed roller and the cutterhead. With no support, the last six inches gets a rippled effect as the end of the board bounces up and down. While it's no great shakes with common framing lumber, you can see where one wouldn't want to have to add six or more inches to each length of exotic hardwood.

    Biggest problem with scraping is the wear is going to be localized; which means 90% of the surface needs to be taken down. The machinery builders grind these tables, shouldn't be any reason not to recondition them on a grinder. They typically are supported on either wedges or leveling bolts, so any bow or twist can be taken out.

    Dennis
    I think snipe may be the problem he is having. He will probably try to get the bed ground somewhere though it could be done on a large mill but not as accurately.

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    Powermatic 221 2" Straight Knife Planer | The Equipment Hub

    I actually ran THAT EXACT PLANER when I worked in a building maintenance shop years ago, and yes, we had a problem with snipe. Since management was never going to fix the planer, our solution was, when it was imperative to not have snipe, run the work through on an auxiliary table that looked like a wide T square; a piece of Formica covered particle board with a cleat to hook on the end of the table. Problem was, covering the bed rollers only worked for rather light work, so was a kludge rather than a solution, but it got the job done. Wonder if he could pick up a second table off a scrapped planer to have re-conditioned before he breaks his down?

    Dennis

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    Quote Originally Posted by Modelman View Post

    ...............Normally when tables wear, it manifests itself as "snipe" in the work; the wood is happily running through the planer supported by the feed rollers, then as the end comes off the roller, it drops down because the table isn't there to support it. It affects the last six or so inches, whatever the distance is between the infeed roller and the cutterhead. With no support, the last six inches gets a rippled effect as the end of the board bounces up and down. While it's no great shakes with common framing lumber, you can see where one wouldn't want to have to add six or more inches to each length of exotic hardwood.....................

    Dennis
    I have a 1940 4" X12" Parks Wood Plane. I refurbished it when I got it around 1973. I've experienced the "snipe' as you call it when I've used it in the past. The table was very flat as I recall but with careful adjustment of the rollers I was able to minimize it.

    I was using it to make guitar backs, sides and fingerboards. Since the rough cut wood was rather thin anyway, I was able to avoid the problem of sniping by using carpet tape to hold the parts to a longer piece of MDF. It worked very well but I recognize that the machine in question is quite a bit larger.

    I didn't know the term"snipe" for the condition that you describe. I referred to it as a "signature cut" since it was the last thing that happened when the wood went all the way through the machine.

    I agree that some sort of grinding would be the way to go but I'm also concerned that the table mentioned here might change its shape when unbolted from its position on the mounts.

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    I end snipe is not an issue with my planer. I don't use a out feed table. Instead I apply upward pressure on the board at the very end of the feed. That would be when the board leaves the pressure strip/roller in the front of the blade. I usually only do this on the final few passes as I bring a thickness down to final dimension.

    (My woodworking used to be measured with a ruler with sixteenths. Now I use my caliper and get to thousandths.)

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    The table on that planer is supported by 2 jack screws, it shouldn't move at all from being unbolted or re-installed. I would check it carefully with a precision straight edge and map the surface. I'd think the real problem will be not distorting it when clamping it down to the grinder or mill.

    As far as eliminating snipe, good luck with that. I think the way to go is by eliminating the bed rolls and using rubber covered outfeed rolls, like Martin does. The Powermatic is a sturdy and reliable machine, but there are better planers out there.

    On edit - If this was my project, I'd deal with the table first and make sure a snipe free cut was possible before investing in that insert head, which will cost about what the planer is worth.

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    Quote Originally Posted by richard newman View Post
    The table on that planer is supported by 2 jack screws, it shouldn't move at all from being unbolted or re-installed. I would check it carefully with a precision straight edge and map the surface. I'd think the real problem will be not distorting it when clamping it down to the grinder or mill.

    As far as eliminating snipe, good luck with that. I think the way to go is by eliminating the bed rolls and using rubber covered outfeed rolls, like Martin does. The Powermatic is a sturdy and reliable machine, but there are better planers out there.

    On edit - If this was my project, I'd deal with the table first and make sure a snipe free cut was possible before investing in that insert head, which will cost about what the planer is worth.
    I once investigated the possibility of changing to a helical cutting head for my Parks Plane. There were universal units available that could have been pressed onto the drive shaft. The cost was out of sight, however. More than 5 times the $200 that I paid for the unit in it's original state of disrepair. LOL

    Also, with the numerous helical cutting inserts, maintaining such a head could become a nightmare. Unless perfectly aligned the results might not turn out well. Sharpening and reinstalling the three blades on the Parks is relatively straightforward and gives good results.

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    Quote Originally Posted by richard newman View Post
    The table on that planer is supported by 2 jack screws, it shouldn't move at all from being unbolted or re-installed. I would check it carefully with a precision straight edge and map the surface. I'd think the real problem will be not distorting it when clamping it down to the grinder or mill.

    As far as eliminating snipe, good luck with that. I think the way to go is by eliminating the bed rolls and using rubber covered outfeed rolls, like Martin does. The Powermatic is a sturdy and reliable machine, but there are better planers out there.

    On edit - If this was my project, I'd deal with the table first and make sure a snipe free cut was possible before investing in that insert head, which will cost about what the planer is worth.
    Thanks for the good advice. As for milling or grinding it and holding it down without distortion,
    it seems to me that it could be mounted on the table of the mill or grinder without clamping it down vertically and inducing distortion
    but could simply be clamped securely laterally to prevent sideways movement and made parallel to the plane of the machine table with jackscrews. The table is so heavy that I imagine it would not move when facemilled or ground with incremental light cuts if clamped laterally. I have no experience with large machines or workpieces though.
    T

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    Quote Originally Posted by LFLondon View Post
    Thanks for the good advice. As for milling or grinding it and holding it down without distortion,
    it seems to me that it could be mounted on the table of the mill or grinder without clamping it down vertically and inducing distortion
    but could simply be clamped securely laterally to prevent sideways movement and made parallel to the plane of the machine table with jackscrews. The table is so heavy that I imagine it would not move when facemilled or ground with incremental light cuts if clamped laterally. I have no experience with large machines or workpieces though.
    T
    .
    .
    typically part is mounted on 3 supports at the Airy points or based on weight and density (not everything is cube shaped) the best spots to minimize sag. even if you machine 4 trim fixture pads so you know they are planar the object you put them on might not be flat. standard practice is to have indicator setup so as you tighten bolts then see if you got soft foot or need to put a shim under to prevent distortion while tightening.
    .
    by using feeler gage stock if you use .0010 ,.0012 and .0015 on different ends you can shim a part in .0002, .0003 or .0005 increments
    .
    cnc milling of flat planar and perpendicular to .0005" per 40" is standard and done everyday. .0003" waviness and lap tolerance done everyday. i often machine mill parts .0005" at a time when i got distortion problems after lowering bolt torque. machining at 30 in/lbs which aint much i often do
    .
    when magic marker marks get thin or start to get transparent you are removing .0001 to .0002 depends on surface roughness
    .
    holding .0002" tolerances is tough. machine warmup can easily cause changes of .0002" there are limits to anything
    Attached Thumbnails Attached Thumbnails warpageremovingflat.jpg  

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    I think a tolerance of a couple of thou would be more than good enuf for a woodworking planer. Just need to get a grinding shop that takes the time and effort to set it up right.

    As to the helical heads, I have Byrd shelix heads for my shaper and in a 6" Powermatic jointer - they are wonderful. They can handle ultra curly hard maple without tearing out at all, and stand up really well to abrasive exotics. I'd put one in my 20" SCM planer if it didn't cost over 3K! I bought a 12" Boice Crane to turn into a super planer with Byrd head, rubber outfeed rolls, and DC variable feed motor, but may never get to it - the wide belt does just fine

    The head in my jointer is perfectly aligned and leaves a great surface, with peaks and valleys of about .001, easily sanded or handplaned out. The shaper head was not so good, valleys of .005-.005" about 1" apart. I indicated it and found the bore was .0025" off center, kinda hard to believe with cnc manufacturing. I bored it out oversize and put in appropriately eccentric sleeves and corrected it. I later was told that the journal Shelix heads were much more consistent. My shaper head is over 10yrs old, maybe they have it down now.

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    Quote Originally Posted by DMF_TomB View Post
    .
    .
    typically part is mounted on 3 supports at the Airy points or based on weight and density (not everything is cube shaped) the best spots to minimize sag. even if you machine 4 trim fixture pads so you know they are planar the object you put them on might not be flat. standard practice is to have indicator setup so as you tighten bolts then see if you got soft foot or need to put a shim under to prevent distortion while tightening.
    .
    by using feeler gage stock if you use .0010 ,.0012 and .0015 on different ends you can shim a part in .0002, .0003 or .0005 increments
    .
    cnc milling of flat planar and perpendicular to .0005" per 40" is standard and done everyday. .0003" waviness and lap tolerance done everyday. i often machine mill parts .0005" at a time when i got distortion problems after lowering bolt torque. machining at 30 in/lbs which aint much i often do
    .
    when magic marker marks get thin or start to get transparent you are removing .0001 to .0002 depends on surface roughness
    .
    holding .0002" tolerances is tough. machine warmup can easily cause changes of .0002" there are limits to anything
    None of which has anything to do with the OP's problem or solution. First remove the offending table and put it on 3 points, Equal in height is what matters , airey points be damned, and check flatness. The surface to be checked must be on the 3 points and checked from below. IF the flatness is .003 or less then the problem is most likely in the restraining when mounted. You can mill, grind, lap til you are blue in the face but if you pull it back out of shape mounting it then you have just wasted time and money. If it is still out on 3 points ten grind it and mount on double sided tape. A magnetic chuck will pull it out of flat, maybe worse. On reassembly if any bolt or screw does not line up with out effort then you are pulling it back to the shape you started with. Find the problem first.

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    When I worked in the lumber mill the planerman would sign me over for OT and we would spend seemingly endless hours scraping the old planer's table, all weekend long. It was built in 1905 or so and we would work for 12 hours at a stretch. That planer probably weighs 20 tons at least.
    He never knew about power scrapers and really liked my Biax, after I started my own shop I found him an electric Biax of his own.
    Grind it or plane it and bolt it back together, then set the surface plate on and finish it to a much higher grade of flatness. After that schedule time every year to true it up using the scraper by itself.

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