Deckel FP 3 L


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Survey says: broken taper pin in the down direction of the Z-axis.

Had to get the machine right apart as the feed rod goes inside the saddle where both X-axis and Z-axis feeds are controlled.

Here is the power feed schematic. Circled area is where the pin in question is located.

Here we see the back of the saddle. The two vertical flaked surfaces is where the column mounts to.


First evidence that we are on the right track…



And the culprit.


Found all pieces. None of the sheared off ones did any damage to the gears below - phew.

It is a standard metric taper pin - I don’t have any. I’ll make one out of O1 tool steel.

While I have the mill disassembled, I will check each and every lubrication port/gallery to make sure we have proper operation. There are passages everywhere…


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I chuckled when I saw the manual excerpt. Sounds so much easier. Like changing a light bulb LOL
I guess that's the best case scenario you could have wished for. No broken gear teeth or internal damage.
The machine looks to be in very nice shape internally (and heavy!)


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Yeah, that would have been too easy. The pin in the reference is the main drive to the power feeds. It is as easy as they describe to replace. But of course no such luck for my case… but I found the problem, so good to go.

Yes, the machine weighs in at ~2000kg and is in quite good shape. Not too many places where the flaking is worn a bit thin. I’ll freshen those up as I re-assemble.


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ISO 40 and Deckel 40 with their S20x2.0 external buttress threads. So I guess not technically CAT 40 as you would use them on your machine.

It‘s a mix of internal metric, imperial and the external threads. Just need the correct draw bar. I don’t have one for each type yet.
On my Maho, I don’t have a huge selection of spindle tooling (U2 collets & #40 collets) and on such a small machine head room is tight - so options are sometimes needed. I’m using some of my BT40 tooling, with a homemade “Deckeldapter”, so keeping the same S20x2 drawbar (fair amount of BT40 used on the CNC) - a quick swap of the pull stud . The Deckeldarters can be purchased via eBay.


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I plan on leaving the OE S20x2 drawbar in the horizontal spindle. It is a special telescoping one. The only way to remove / service it is by complete disassembly of the Y-axis head / spindle.

I have quite a bit of NMTB 40 tooling (with various drawbar threads). Plus a more or less full set of S20x2 Deckel collets and the spindle adapter. This makes for a very compact tooling setup. Basically, the tool holder is flush with the spindle nose - so only tool is sticking out.

I will have 3 drawbars for the vertical head: the S20x2, a M16 and a 5/8”- 16.

One of the differences between a Deckel FP3 and my FP3L is the table has multiple height slots it can be mounted to the 45* slant bed. This gives max clearance in Z-axis of 22-1/8”, a Y-axis of 24-3/4”, and X-axis of 31-1/2”.

Here is a picture of the basic mill (center) with all the available accessories.


So far I have only the fixed table, the vertical spindle head, and the overarm support (they call it Outer Bearing). I do have a rotary table and a universal dividing head by other manufacturers.


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No other damage. I bet they bottomed out in Z by using full rapid. It moves the mill head very quickly and there is no brake to stop the motion. The inertia probably allowed the column to continue downwards until it bumped the physical stop with enough rotational feed speed to bust the pin.

Material seems very brittle by the look of the shear faces.

DIN 1 4x26mm shear pin material is “mild steel”. I think I need to change that pin to something other than tool steel.…

Thanks for making me think a little deeper about this pin, Mike.

The last pin I had to make was for the CMT URSUS lathe. There the pin does not have a shear function, rather it is a pin-two-components-together kind of a deal.


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I think so. If it is too soft, it won’t shear properly. The OE pin I took out feels about the same as O1 (or similar) with a file test.

Most farm equipment OEM Shear pins are grade 5 bolts.

Bending failure is not desirable. I see it all the time. Far too many farmers replace broken shear bolts with regular bolts and then the secondary damage skyrockets. Sometimes they use grade 8 too.

So I think you are on the right track.

It's one of those areas where I don't have a lot of design experience but a crap load of field exposure.

Since you don't know for sure what it is, can you do a backwards calculation and substitute different materials? Or is that more work than it's worth?


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So I checked my German Standards Manual and then did a search for the material of a standard taper pin. Here is what showed up:


It seems that the AISI equivalent is 12L13 steel for non-hardened pins.

12L14 is the closest I have in stock but only in 1.5” round. Seems that 1018 has very similar properties to 12L14 in terms of hardness, yield, and shear modulus (but is not free machining do to no lead added). I have 1018 in 1/4” rod. So I will grind a pin out that material.


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Thanks for the offer regarding 12L14 stock Peter.

Yes, I plan on making extras.

I am not sure if the hole has been reamed to a SAE #2 taper pin size. The Metric pin I made does not fit properly. The taper angles are slightly different between SAE and Metric (1/4” per foot vs 1:50).

There is not enough space for my #2 taper reamer to rotate all the way around so that I can examine the thin end for play. So I’ll have to make a #2 taper pin and try it.


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I made a standard metric pin (using the correct taper angle this time… I know, math is hard sometimes…) and it fit perfectly.



Pin installed


Then it was on to the next issue: some of the way lubrication passages were blocked with crud. I used compressed air and and stainless steel lock wire to clear them out. Because of lack of lubrication over some time, the flacking on the Z-axis retaining plates were worn off (left four holes were plugged (green circles)) - they are interconnected with an internal passage to the supply passages (blue circle). Red circles are the through holes for bolts to attach the plate to the column.


After a bit of work, it now looks like this (plate is 180* flipped in this image)


Plates (one for each side - opposite plate shown here) are made from steel, precision ground.


Because I used compressed air to clear the oil passages, I blew out a sight glass (once the crap cleared) in the column. It bounced around the shop at great speed and broke. It is made of acrylic (plexiglass).



I did not have any stock big enough to make a new one so I went and ordered some 1” rod. Learned that there were two types: cast and extruded. You want the cast stuff for machining; if you get the extruded material, it will crack and chip during machining. Did not know that...

Here are some images of the turning process - this was the second attempt.

[The first part was fine except I was off by 0.05 mm on the OD (it is a light press fit into the column bore; mine was too loose) plus I had trouble polishing the inside of the bore bottom. I had used ~1800 rpm and no lubricant - so part needed polishing as the surfaces were “crazed”. Flame polishing worked on the OD, but part got too hot and distorted when I tried the same on the ID].

Second attempt: 1030 rpm, 0.0015 in/rev, water soluble cutting oil (undiluted), carbide inserts for stainless steel.

Much better! Ready for parting off.


This is the stock material after parting. You can see the jaw contact lines and the serrations through the face of the acrylic.


Parted off, ready for a facing cut.


Faced to dimension (No scratch, just a bit of lint on the inside of the bore).


And the ”Three Amigos” (l.t.r.: original, flame polished & distorted first attempt, and final part)


And installed in the column.


Next is cleaning / inspecting the bed…


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I've never thought about using my Spin Indexer on my surface grinder let alone on a big sine plate.......

Yes, it works very well - as long as your surface grinder has the real estate to accommodate the two items.

The proper tool is a punch grinder. They are very compact, super accurate and can be pricey. I don’t have one.



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The proper tool is a punch grinder. They are very compact, super accurate and can be pricey. I don’t have one.

4 grand eh...... Well, that's not showing up in my shop anytime soon.

My list of wants includes some precision indicator rods. I'm not even fussy on the diameter. I have always thought about just making some, so I'm thinking....

I do have some smithing indicator rods (long and short) in the popular calibers, but they are tapered for their intended purpose. I'd like some straight ones.