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Thread: Premeta SL Tool Grinder
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5th Apr 2020, 11:56 AM #1Golden Member
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- Apr 2009
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Premeta SL Tool Grinder
Got this tool a few years ago from a local shop closure with one wheel and one collet.
No other accessories.
Appears to have the same working envelope as a Deckel SO.
Main difference is use of double ended motor with direct mounting of wheel, and the stand.
Benefit is a second wheel outboard for hand grinding.
Motor continues to rotate with single phase applied to each winding in turn, so probably Ok for a VFD.
Motor plate is 230/415 V, 60 cycles, 2800 RPM.
Cannot find any data at all on this tool.
Lathes UK do not list it as a copy of the Deckel.
The company does not come up on searches.
Collet is unmarked and fits 12 mm nicely.
But, there is a pronounced step in the bore 35 mm in.
Is the step normal ?
Started to clean down with paper towels and metho - a daunting task.
Need suggestions on a cleaning method.
Intention is to use it to see if it is fit for purpose.
Perhaps then consider a strip-down and complete refurbishment.
Any suggestions on a source for collets ?
Premeta Collet compr.JPGPremeta Stand compr.JPGPremeta General compr.JPG
John.
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5th Apr 2020, 03:00 PM #2Most Valued Member
- Join Date
- Oct 2010
- Location
- melbourne, laverton
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- 1,910
hi mate. the first photo looks like a deckel collet. simulator.
Has it got a 20mm buttress thread on the end??
I like the look of your machine
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5th Apr 2020, 06:15 PM #3Golden Member
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- Apr 2009
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- Kingswood
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Not sure what you mean by 'buttress' thread.
The collet body is 16 mm diameter, thread is 1.25 mm pitch (definitely not 20 TPI) and 15.1 mm diameter.
Got some 'Grease and Wax' cleaning solution off a mate, and I will try that in the morning.
John
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6th Apr 2020, 08:50 AM #4Senior Member
- Join Date
- Nov 2019
- Location
- Brisbane
- Age
- 69
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- 452
Premeta tool grinder
Hello from BC.
I have used citrus cleaner on machine tools with great success. Wipe off with paper towels then spray with plain water.
Regards
BC
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10th Apr 2020, 12:40 PM #5Golden Member
- Join Date
- Apr 2009
- Location
- Kingswood
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- 930
The Grease and Wax cleaning solvent works Ok, but suspicious about the effect on the skin.
Dug around a bit regarding Deckel collets and buttress thread.
A mate has a Polish clone of the Deckel FP1 milling machine with every extra ever invented.
This includes a high-speed vertical head that uses Deckel collets.
These collets are similar but have a ground end and a buttress thread 12 mm dia x 2 mm pitch.
Then there are the recent Asian grinder clones that seem to be bigger (20 mm ?) with a large diameter buttress thread.
Also, seen references (Lathes UK ?) that Deckel changed collet design at some time.
So: I will have to be careful when looking at possible purchases !
The first operating problem was the inability to clamp the Work Head to the Main Axle,
Dismantled the clamp handle and sorted out how to adjust it.
Several cycles of adjustment got it Ok.
All the other adjustments seem Ok.
Next step is to power it up and experiment with trimming a 12 mm end mill.
John
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10th Apr 2020, 08:22 PM #6Golden Member
- Join Date
- Apr 2009
- Location
- Kingswood
- Posts
- 930
A couple of steps forward, and a roadblock.
Wired motor delta and will test run it tomorrow.
Spindle threads are RH in the work area and LH outboard.
Wheels are Dia 14 mm bore and held by conventional flanges, no taper.
The only wheel is a thin disk, that may be CBN.
The flange bosses that support the wheel have a thickness that adds up to more than the wheel thickness, so the wheel cannot be clamped.
Reversed the outboard flange but the nut will not run up to the flange due to a step in the spindle
Made an appropriate spindle washer and mounted the wheel.
Checked a Dia 12 mm drill to see if that could be sharpened, no way because the step in the collet leaves too much hangout.
Hand held a Dia 12 mm 4-flute end mill against the wheel and imagined how the work head could be set up accordingly, looks doable.
But:
Cannot attempt a job because the main axle will not move axially, only rotate.
The scale on the knob at the end is 0 - 100, so not an angle measure.
In the photo, the large knob at the front locks/limits main axle rotation.
The large knob at the end is locked to the smaller knob and to main axle rotation, seems to me two knurled knobs like that should move relatively.
Suspicion falls on the grub screw and nut at the front, I will investigate that tomorrow.
May have to remove the unit from the base to investigate the internals.
Also, the dresser cannot be adjusted axially, there is a shaft supporting it with a knob, but it doesn't work.
Main Axle Knobs Compr.JPG
John
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11th Apr 2020, 01:20 PM #7Golden Member
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- Apr 2009
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- Kingswood
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The roadblock is clearing, got the Main Axle out after some work.
Investigated removal of the machine from the base, and found two bolts LH and one RH.
First removed the bolts from LH, loosened the one RH and rotated the machine on the stand (carefully) until I could inspect under the knob control area.
Nothing there, all solid casting, so back in went the bolts.
Then removed the 3 grub screws: small axial knob, front control area and main axle clamp boss.
The smaller axial knob one interfered with the ring on the adjacent larger scaled knob, but persevered leaving scars in the larger knob.
The axle could then be pulled out.
No obvious damage, no corrosion and adequately greased.
Playing on the bench, the two knobs do rotate relative to one another and the scaled knob does adjust axially.
It operates by advancing the bearing supporting the LH end of the main axle.
The smaller knob may be adjusting rotation while the larger one adjust axial movement.
On reflection, I think there was in fact nothing wrong, just lack of knowledge !
The front control grub screw enters a recess on the barrel preventing its rotation, and so stopping axial movement.
Not sure what the other two grub screws do, yet.
It could be the grub screws change operational mode depending on the customer's requirements.
Still have not yet clearly understand the modes, but confident that is the answer.
Chatted with a friend and he explained that he made the seven collets for his Clarkson T&CG.
His were ground internally on the lathe, but we agreed a reamer would be adequate for my requirements.
Also, as my wheel is brown in colour it is probably diamond.
Correction to an earlier statement, the wheels are 20 mm bore, not 14 mm.
John.
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11th Apr 2020, 06:22 PM #8
Hi John,
Nice looking grinder, should prove very useful.Best Regards:
Baron J.
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11th Apr 2020, 08:02 PM #9Golden Member
- Join Date
- Apr 2009
- Location
- Kingswood
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- 930
Well, the lack of understanding shows.
It turns out all the grub screws should be fully home for the machine to work correctly.
The grub screw in the smaller knob at the LH locates that knob to the main axle.
The front grub screw locates the barrel, the item that carries the bearing with the main axle thread.
The grub screw at RH on the main axle boss prevents an internal split sleeve from rotating.
When re-assembled and all grub screws inserted, the two knobs work as expected, smaller one rotates the main axle and the larger provides axial.
I think the problem observed by me was the front grub screw had been withdrawn, allowing the barrel to rotate, so no relative rotation with the larger knob to provide axial movement.
But, the knob friction evident when assembled indicates to me that I need to dis-assemble further and clean it up to make it acceptable.
On the bench, friction seems Ok, so still a bit of a mystery.
A further issue is to decide just what is the median position of the barrel, perhaps the high friction is because I have it too close to a limit case.
The machine has a recess somewhat like a keyway in the main axle with radial sides that is engaged by the front control knob adjustable spigot.
If the knob is fully in, the main axle is prevented from moving.
If the knob is fully out, the main axle can rotate.
When the knob is partially inserted, the knob spigot interacts with the sloping sides of the recess to provide an adjustable limited arc of travel.
The spigot has scars from contacting the slope edges, and the slope side edges have burrs picked up by the spigot..
The maintenance attempted was to stone off the burrs on the main axle recess, a small amount of EP grease added to the recess, and the knob spigot stoned off in the lathe.
This week, I will seek a source for CBN and diamond wheels. Gasweld and Blackwoods first.
I have dismantled the work head and intend making an accurate record of the collet head dimensions with a view to designing and making a head that accommodates something different to the Deckel collets.
If ER32 collets, I could freshen up the cutting lips on cutters of any size up to 20 mm.
Another issue are the nuts on the spindle, how does one get them off ?
There is no way of holding the spindle, one LH thread and the other is RH.
The Deckel and clones have a hole through the spindle and a matching hole through the spindle housing for a rod to restrain the spindle.
Any suggestions on what I could do ?
John.
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11th Apr 2020, 08:24 PM #10
Hi John,
I would have thought that the wheel head is just like any double ended grinder, you just grab the wheel and loosen the nut. So yes one end will be left hand threaded and the other a normal right hand thread.
At least unlike me who got an 8" grinder without wheels from the scrap yard and had to make a left hand nut to fit the threads on the spindle. It took me several goes to get a good one, till I had figured out that I had to thread from the back.Best Regards:
Baron J.
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11th Apr 2020, 10:27 PM #11Golden Member
- Join Date
- Apr 2009
- Location
- Kingswood
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- 930
Grabbing the wheel in this case is a tad difficult, it is 2 mm wide over the working area.
Have found a fundamental engineering problem.
The Work Head clamp to Main Axle is too loose.
The photo shows the housing on the axle, and it has a noticeable loose rocking motion.
A clamp applied requires a lot of force, and visible distortion of the casting, to effect a clamping action.
This explains the difficulty I had initially to adjust this clamp action.
The axle measures 24.98 to 24.99, and seems uniform.
The problem is the casting.
The casting is 35 mm diameter at minimum.
It would be easy to bore out the casting to some nominal size, but what to use for the inserted liner ?
The resultant thinness of the liner might possibly rule out Cast Iron, but Bronze doesn't seem correct either.
Would mild steel be an acceptable compromise ?
Just how thin can CI be and still be a good engineering solution ?
I think I could make and glue in a 1 mm thick sleeve, probably with a full length split.
Are there any other options ?
Work Head Clamp to Main Axle compr.JPG
John.
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12th Apr 2020, 06:10 AM #12
Hi John,
You are going to have to be careful with that casting if its become that loose. You could put it in the vise and with nothing in the bore very carefully squeeze the slot closed a little. The cast iron will bend but not by much.
If you wanted to be sure of not cracking the casting you could turn a plug, say 20 thou (0.5 mm) smaller than the bar that would normally go in there, put that into the bore while squeezing it and see if you can cause it to close up enough to make it a good fit. Then when you tighten the clamp bolt it should grip firmly.
You might have to take another 20 thou off the plug if its not enough first time round.
Actually the correct thing in there would have been a split cotter. That would give a half a turn from loose to locked without stressing the casting.Best Regards:
Baron J.
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12th Apr 2020, 12:01 PM #13Golden Member
- Join Date
- Apr 2009
- Location
- Kingswood
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I think squeezing the casting in a bit, or adding a cotter pin, do not solve the initial problem, the casting is bell-mouthed at both ends.
I checked the automobile engine sleeve catalog by Darton in the US.
The absolute minimum wall thickness noted was 0.071" = 1.8 mm.
This is listed for a Mitsubishi that has a piston size of 3.338" = 85 mm.
The material is centrifugally cast ductile cast iron.
The only material I have in stock is extruded CI, so a bit more thickness might be required.
But, my application is nothing like an engine, so perhaps 1.5 mm would be Ok.
This requires me boring out to 28 mm in a casting that is 35 mm, leaving 3.5 mm thickness.
Does this sound like a reasonable approach ?
If the sleeve like this is implemented, should I split it full length ?
And/or glue it in place ?
John
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12th Apr 2020, 06:32 PM #14
Hi John,
If you are going to all that trouble to make a repair, why not just make a new one from steel !
I wouldn't bother trying to copy exactly, but make a functional equivalent. A good turning exercise too.Best Regards:
Baron J.
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14th Apr 2020, 10:32 AM #15Golden Member
- Join Date
- Apr 2009
- Location
- Kingswood
- Posts
- 930
Some progress, but the project has been delayed.
The photos show the squareness test on the surface plate and the intended work-holding for the boring.
I 'assumed' the end face would be square to the casting bore, but the test on the surface plate showed otherwise.
As the casting had to be mounted above the mill table for cutting bit clearance, the rather thick parallel was used with a shim to achieve squareness.
The horizontal rotating joint was installed, the scale set to zero degrees and the joint set parallel to the surface plate on a couple of matched HSS stock bits.
The engineer's square immediately showed the error, corrected by the paper shim.
The rotating joint was then removed and replaced with a newly made spacer that duplicated the size and fit of the rotating joint.
The casting was then pulled up tight to the angle plate, which of course, will be transferred to the mill for boring.
Then, a problem.
Tried to set up my brand-new boring head in the mill only to find the boring head dog slots would not engage the quill dogs.
This subject is the described in a thread in the General section.
So, it will be a day or so before progress can be made.
Head Clamp Face Squareness compr.JPGHead Clamp Boring Mount compr.JPG
John
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