Blanchard grinding

[Peter Kelly]

The cast surfaces on my SCMI machines almost certainly face-milled, not ground. Process is similar to below.

[Rick Fisher]

I prefer the planed finish. My old SCM Bandsaw has it .. Jointer and soon to be planer ..

Martin and Panhans still do it .. I think Griggio still does too. I think its a step up .. probably adds to the cost..

[Rick Fisher]

I read an article one time about the foundry which SCM owns. It alleged that the SCM foundry was one of the most advanced in the world and did some of the finest work. Apparently they made castings for companies like Ferrari, Whirlpool etc. And most notably for the mechanism which held high speed trains to the tracks. ( kinda a big deal)

Its likely that SCM / Mini Max is more than capable of producing whatever is needed or whatever they deem needed for woodworking machinery ..

[Derek Arita]

Just had my MM j/p Blanchard ground. Although it did produce decent results, it did not produce perfect tops...within .005". It was very costly, primarily because a jig had to be welded up to hold each table while being ground, then the jig had to be ground flat itself. Sounds like an engine shop may produce better results and whole lot cheaper. That's the way I'll go if I ever have to do it again.

[Jamie Buxton]

Do you really need to grind the whole table surface? Or do you just have a little weld bead above the plane of the rest of the table? If it is just a little bead, you can knock that down with a right-angle grinder, or even by hand with a metal file.

[ian maybury]

To the original point.

Blanchard grinding is just one option - one that's seems often to be used because it's meant to be relatively cheap, is set up to rapidly process large quantities of flat work, can seemingly make the required tolerances if the machine is in decent nick and properly operated, and the machines tend to come in sizes that handle large surface areas. It's a Lumsden grinder over here by the way, but the principle is similar. One risk is that they are typically used for volume work, and operators are not necessarily machinists or used to putting in the required care on set up.

Conventional surface grinding (with a grinding wheel mounted on a horizontal spindle - there are some big ones) is sometimes an option, but the reality is that most toolroom type surface grinders have neither the stroke nor the width to handle machine tables. As a machine they (even if can find a big enough one) perhaps sacrifice some cost effectiveness for additional capability beyond just whizzing over large flat surfaces.

Shaping and milling are other valid options - although the latter at times is forced beyond reasonable depth of cut and feed limits and results in very poor/grippy/ridged surface finishes. It can also result in out of flat tables as the cutting forces are potentially quite large.

Fixturing is a big issue. Cast iron tables are much more flexible than most of us think, and if a magnetic chuck and/or cutting forces over an improperly adjusted support fixture result in deflection the table will likely look great but be way out of flat when it's afterwards released and it springs back.

Shiny tables are nice, but the fact in the end may be that stoning back and/or sanding followed by wax can deliver an acceptable surface in almost all cases provided they are basically flat. I'd argue that choosing a skilled machinist that will do the job right/carefully and has a sufficiently capable machine is probably more important than the choice of process.

I've just finished reworking a set of Hammer A3 410 tables scraping by hand. Not because it was good use of my time (or a realistic option for most - it needs some equipment, there's lots of scope to screw up, and it's bloody hard work), but because (in a small country) i couldn't get the tables done by others - the only two quotes (there's only a few Lumsden's and/or surface grinders big enough to do the job here) were very expensive, and the 'sure no problem' type attitude to fixturing didn't inspire confidence. The method has the adavantage (given a good reference surface and correct technique) of being able to achieve flatness far beyond what's needed on a jointer.

Table flatness tolerances are the other big issue. It's commonplace in some quarters to talk of woodworking not being a precision activity (perhaps not if you are planing skirting boards), and to laugh at talk of high accuracy machine set up (and it suits machine makers to set the tolerances enormously wide, and to promote this line of thought so that it will be passed on) - but the hard fact (based on my own experience) seems to be that more than a couple of thou (0.002in) out of flat in the wrong part of a jointer table can very noticeably influence the line of cut when jointing.

At it's most basic level straight jointing entails flat and coplanar tables, the infeed set below the outfeed by the depth of cut and knives accurately set a whisker above the outfeed table. No more, no less.

I'd argue that most jointer cut line problems and inconsistencies originate with out of flat and misaligned tables (presuming the cutter is properly set up) - and that if after alignment is sorted the tables are not flat there's typically no amount of playing with technique and/or settings that will deliver consistent results to the standard that table size should be capable of. There's for example not much point busting a gut trying to set knives to the often recommended 0.001in above the outfeed table if that same edge of the table is out of flat by e.g. 0.005in.

I'd also argue (sorry - feeling that way today) that technique can matter a lot, but mostly when either jointing wood that isn't straight, or over tables that are not flat - when tipping it forward or back or to the side can alter the line of cut. Straight wood over flat tables seems pretty straightforward. Lots of us i think get talked into a tailspin over technique when again the issue is more often basic table flatness and machine set up...

[Ronald Blue]

I am not saying there aren't Blanchard grinders using segmented wheels but the ones I ran used a one piece wheel formed in a ring. The advantage of the Blanchard is the speed in which you could surface large pieces. Extreme accuracy is possible but becomes time consuming which negates the advantage. I would think a competent automotive machine shop could give more than acceptable results also. Good luck with the project.

[Marc Coogan]

After the shop looked at the picks of the table they were thinking milling the tables would be a better option. It looks like the table was hit or dropped the ear that sticks out around the blade was broken of and welded back on about 10" in length

[Tony Zaffuto]

Ian's post #23 gives an accurate appraisal of the most important factor: fixturing! If whoever does the job is inexperienced or even worse, rushes without care, regardless of whether ground, milled or whatever, the results may be substandard. Before deciding who will do the job, visit and take the table section with you so the shop (preferably whoever will be doing the job) can look it over. Tell them the tolerances you want (and where) & let them decide how to achieve them.

As a point of reference, through the 90's and until 2004, I was the owner of a very large machine shop, and then merged in with a much larger plant, with metal stamping operations. We had a blanchard grinder, several planers along with dozens of other machines. I sold my interest and now reside in a powder metal manufacturing plant (only owner) in which I have a complete tool making facility and secondary machine shop (mainly CNC).

[Derek Arita]

Don't mean to stray, but a friend of mine said he once flattened a PM66 table with a 12x12 piece of 1/2" thick glass and sand paper. He said he worked on it for days, but finally got it down to within a couple thousandths of dead flat. He said that this was an acceptable way of doing this..was he yanking my chain?

[Tai Fu]

Of course you can. If it's really out of flat you could even use an angle grinder to grind off the high spots (using something flat as a reference), then when you get close grind it with a piece of sandpaper fixed to something flat. The catch is it does take a LOT of time, sandpaper, and muscle.

[Derek Arita]

Of course you can. If it's really out of flat you could even use an angle grinder to grind off the high spots (using something flat as a reference), then when you get close grind it with a piece of sandpaper fixed to something flat. The catch is it does take a LOT of time, sandpaper, and muscle.

Does it take a great deal of experience or just patience and monitoring?

[Tai Fu]

I would say both.

[ian maybury]

I'd seek out somebody able to do a good grinding job if i could - probably a low overhead small shop/one man band with the right kit and skills that will put the time in to do it right without charging more than the job is worth - but i'd need a lot of convincing about the fixturing method. (see below) I hand scraped my tables. There's nobody offering the service here - but it's still used when reconditioning machine tool ways and the like. I wonder if it might be an option if you are in the right part of the US to use a commercial hand scraping operation to do your tables? Don't know how many there are about like these guys: http://www.youtube.com/watch?v=nOJrhrne80s

The fixturing problem when grinding arises from the fact that the table needs to be supported from underneath at multiple contact points in the relaxed state from what is a rough cast under surface - which is why as somebody said earlier a common approach is to create machined contact areas for the fixturing to bear on underneath. Trouble is that this operation is itself is subject to the same problems.

I've a feeling that a jig with multiple threaded/adjustable support points might be an option, but getting that dialled in properly would still be a tough job without a very precise overhead traverse/xy deal from which to mount a dial gauge. It's a bit scary how flexible a solid looking cast iron table actually is - experience from setting up my own A3 410 has shown that even finger tightening of support screws applies enough force to cause deflection of several thou.

It meanwhile takes an awful lot of DIY work with an orbital sander to remove detectable amounts of material over a largish area - but just a momentary indiscretion with something that removes metal faster to cause a gouge - and there's still the problem of detecting what's flat and what's not.

A good engineers reference edge and feeler gauge will pick up issues in a given line, but right method is needed (measuring across the diagonals with a full length edge, and maybe more) or twisting may be missed. The other method is to use a precision level and accurately ground parallel bars, but it needs a lot of care. The real deal would probably be to get it under a 3D xyz co-ordiate measuring machine on a 3 point support as is sometimes used in large toolmaking operations.

The hand scraping option while not normally used on large surfaces is from personal experience a very valid option that side steps most of these problems. Subject to the cautions (!!!!!) above it may even for some for some be a DIY option - you need a reference surface/surface plate and the right (carbide) tools, ideally the means to lap/sharpen them (not too hard to DIY from info on the web), it's several days very hard work for a fit person (both the scraping and lifting the table on and off the surface plate for rubs), it's skilled, and there's scope to mess up/be left with unusable tables and require grinding or something to sort it out. Don't expect a machine maker to honour the warranty if you've removed and scraped the tables...

Against that it can be done to the level required from a standing start if you have good aptitude, read up carefully in advance (attending a course or two would be even better - there's at least a couple on the web offering them and how to manuals in the US), run a few test pieces and have the ability to apply enough method and experience to keep control of the variables and not mess up. The other very helpful development in recent times is that a large toolroom quality granite surface plate (it needs to be as large as the table to be flattened) can be bought these days for not much more than the cost of shipping it.

The big advantage in the context of the fixturing issue is that it works on a free standing table, so unless there's an issue with locked in casting stresses or something it's straightforward enough to take the table to within less than a thou all over. A beginner probably won't develop the skills (requires a particular stroke) required to produce the highly attractive look that an experienced guy can, but it can still be nice - and stoning off with a diamond plate or whatever quickly (because it only has to cut off the tips of the high spots) is relatively easy.

It's laborious, because each cut strips off only at most about half a thou in the areas cut - and it's not unusual to find high areas up to 0.010in and more if the table is twisted. Small hollows are the real bad news, as going after them entails multiple cuts over the entire area of the table….

[Joe Kaufman]

I would suggest that you need to determine the base line or existing condition of your machine. At a minimum, clean up and inspect the sliding gib surfaces. Assure that there are no cracks in the castings in these areas. Can the gibs be adjusted for almost zero clearance and will the tables move through the distance or travel that you expect without excessive clearance? Are the tables co-plainer in the normal operating position? You will have to determine what you will settle for. You will need a good 4’ straightedge for this. Using a engine rebuilders head surface grinder (probably the most cost effective method) may achieve the surface finish you desire but there will be nothing to assure what the assembled co-plainer result will be.
Keep in mind that a “Blanchard Grinder” or equivalent is similar in function to a thickness planer for woodworking. It will make two surfaces parallel or the same thickness. As previously stated, providing the work holding and surface reference is no simple task. An automotive head surface grinder is similar to a jointer in that it will make one surface flat but usually without reference to any other surface.
I believe most new jointers are assembled, adjusted and then both table surfaces are ground at one time as a complete unit.
My prospective on older used equipment may be biased since I was involved in Plant Engineering and Facilities for several years. I have witnessed the handling of excess/surplus equipment. It’s usually get the old equipment out ASAP, it’s in the way of the rearrangement and new equipment installation. Plant closings are not much different, clear the floor so we can close the lease or put the building on the market. Bids will be taken on the equipment in the parking lot. A few months ago, I went with a friend who was looking for a Unisaw to a surplus equipment dealer. The Unisaw was brought to the viewing area by forklift, one fork under each extension wing. I have seen jointers treated similarly.
Joe