Author Topic: Frustrating Day  (Read 12918 times)

Offline Roger B

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Frustrating Day
« on: December 15, 2013, 07:34:05 PM »
I have been having problems getting good finishes on the CI bits I have been machining recently. I wasn't sure if it was a problem with the tools, the lathe or my skills. I played with different tools, different feeds, and different speeds without success so final decided to install the pair of Japanese taper roller bearings I had bought for my Mini Lathe to replace the Chinese ball races.

I had read David Fenner's Book and the Arc website but was also aware that my lathe was one of the 'other' Chinese ones (Extended lead screw, two clamp screws on the tailstock, gear cover on the apron) so was prepared for the worst. I made two 1.2mm spacers to compensate for the difference in the size of the taper roller bearings against the ball races and started to dismantle.

First problem: The gears would not come off the mainshaft and jammed against the countershaft gears. As these were plastic gears I had to remove the headstock and the counter shaft to get it apart. By this time basically all that was left was the bed.

Second problem: When I put it back together I could not fit the Tumbler gear on the mainshaft as the  plastic spacer was 2mm too long. With a working lathe no problem. With a dismantled lathe big problem  :(  . Luckily it was a press fir over my smallest Rohm chuck and I was able to machine the 2mm off in the drill press using a wood chisel (super bodge  ;) )

Third problem: When I removed the leadscrew to get at the bolts to remove the headstock I found that the length between the bearings was incorrect. This is a problem for another day  :'(

Finally as almost everything else was dismantled I thought I should check and adjust the various slides. The lathe bed is nicely ground, the saddle is very roughly milled  :( Another job for another day.

Maybe my thoughts about buying a German lathe have come at the right time  ;)
« Last Edit: December 16, 2013, 07:39:38 PM by Roger B »
Best regards

Roger

Online sco

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Re: Frustrating Day
« Reply #1 on: December 15, 2013, 09:04:06 PM »
I had the same sort of frustrations with my sx2 mill.

Get a wabeco lathe - i love mine!

Simon.
Ars longa, vita brevis.

Offline ths

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Re: Frustrating Day
« Reply #2 on: December 16, 2013, 05:07:41 AM »
I assume that's an oil way in the bottom of the saddle in the last photo? It does look fairly 'rugged' under there.

Hugh.

Offline Roger B

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Re: Frustrating Day
« Reply #3 on: December 16, 2013, 07:38:54 PM »
It's a bit rough under there. I will see what I can do with a smooth file. I could try to learn scraping (or scrapping  ;) ). I think most of the problem was the two ballraces. If I held the inner races down on the surface plate I could lift the outer races more than 0.1mm, not exactly high precision. I think that there was some preload taking up the clearance. When I was trying to turn a biggish lump of CI I got better results cutting towards the tailstock, the rotating centre probably had better bearings.  :)
Best regards

Roger

Offline steamer

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Re: Frustrating Day
« Reply #4 on: December 17, 2013, 12:59:22 AM »
Don't smooth it.  It's better for it to be a little "rough".  It will hold the oil better...much better than a draw filed polished finish.

Additionally, unless you measure what you're doing, your going to do more harm than good filing it..it is easy to get the saddle out of alignment with the headstock.

...and it's scraping...... 8)

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline Roger B

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Re: Frustrating Day
« Reply #5 on: December 17, 2013, 07:42:41 AM »
I don't intend to do much to it, but from the rubbing marks there looks to be almost point contact at the left hand end of the V slide. I'll blue it and see whats going on then decide what to do.

When I have been using the lathe I have had the feeling that the flat side and the V side are not quite parallel causing the slide to rock or twist. This can be felt especially when milling due to the interupted cutting. I will have go at making it a bit better, remembering that it is a cheap lathe. I could by a new one for the cost of a bed grind as mentioned on the old Myford thread  ::)
« Last Edit: December 17, 2013, 08:26:33 PM by Roger B »
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Roger

Offline Roger B

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Re: Frustrating Day
« Reply #6 on: December 17, 2013, 08:38:29 PM »
I had a go with the blue and took of the worst high spots with a fine file, put it all back together and spent about 15mins adjusting the slide. It feels a completely different machine  :) . I needed to make a new spacer to replace the bodged one and was able to take cuts (in aluminium) that stalled the motor with no sign of chatter or vibration. Totally different to making the two bearing spacers from the same material before I took it all apart.  :DrinkPint:
Best regards

Roger

Offline smfr

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Re: Frustrating Day
« Reply #7 on: December 18, 2013, 01:23:34 AM »
Nice improvement! That splash of yellow paint on the base cracks me up every time  :ROFL:

Simon

Offline steamer

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Re: Frustrating Day
« Reply #8 on: December 18, 2013, 10:10:25 AM »
Roger,

Glad it's working out for you.   To measure the alignment of the saddle with respect to the spindle is pretty simple to do...even in a home shop.

You will need

A 4 jaw chuck.
A milling machine parallel that is STRAIGHT!...A 6" long one will do.
A dial indicator and fittings so that you can reliably fit it to the cross slide.  A .0005" is good... A .0001" indicator is better.
The lathe powered OFF...and unplugged!

Mount the 4 jaw and invert 2 opposing jaws
Mount the parallel in the chuck as shown


Mount the dial indicator, and crank the cross slide to the back and zero out the indicator on the face of the parallel.

BY HAND, rotate the chuck 180 degrees, and check the reading....bump the parallel until you get the same reading on the indicator regardless of the position of the chuck
Once you get Zero-Zero....the face of the parallel is perpendicular to the axis of the spindle...it can't be anything else.

With me so far?

NOW the real measurement begins!

Rotate the chuck until it's horizontal....like the picture above, and the indicator is zeroed against it.   Now run the cross slide out towards you to the other side...or at least as far as your cross slide travel will allow


Don't adjust your parallel!....What does the indicator say?
The reading on the indicator is TWICE the error in perpendicularity of the cross slide axis with respect to the spindle axis.   You should have a positive number...say about .0004" in 6" of cross slide travel...or .0002" in 3"....that ratio.  Depending on how much cross slide travel you have.

That ratio is twice the error.   so in reality it would be an error of about .0002" in 6" turning concave  "Hollow in the middle"...NEVER convex...or crowned in the middle.

That is why I caution you to go easy with a file in the saddle area of the lathe....that saddle surfaces are very sensitive to metal removal....ie you don't have to move much metal to move the saddle quite a bit.   Especially on the V ways.....it's very easy to turn the saddle.

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline steamer

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Re: Frustrating Day
« Reply #9 on: December 18, 2013, 10:18:27 AM »
You'll notice I used a 3 jaw....it doesn't matter...just as long as you have a hold of the parallel....it'll work.

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline modeng2000

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Re: Frustrating Day
« Reply #10 on: December 18, 2013, 02:32:11 PM »
Very helpful! Now I have something else to worry about 'till I can get round to measuring it.

Many thanks,
John

Offline Roger B

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Re: Frustrating Day
« Reply #11 on: December 18, 2013, 08:32:34 PM »
Dave,

Thank you for that. I don't have any solid parallels, just wavy ones. I found a piece of aluminium bar and checked it on the surface table. It was flat + 0.01mm.

I set it up in the 4 jaw chuck and put my dial gauge in the tool holder. As near to the operator side as I could get the bar was again parallel to a similar tolerance. I then wound it in to the centre, about 50mm and the gauge reading increased around 0.08mm.

It is definitely cutting concave, but perhaps a little more than is nice. I know it has always had tendencies this way. The camshaft housing on my vertical engine has two turned flat faces together, made before I started playing, and as best as I can judge with feeler gauges there is a 3-4 thou gap in the middle of a 2" piece.

After this I put my lump of CI back on the Keats and could actually get a good finish!
Best regards

Roger

Offline steamer

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Re: Frustrating Day
« Reply #12 on: December 18, 2013, 11:33:11 PM »
Good!
Always good to know whats what!

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline Roger B

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Re: Frustrating Day
« Reply #13 on: December 27, 2013, 09:19:11 PM »
I hope everyone had a good Christmas with electricity most of the time  :stir:

While turning the valve blanks for my 25cc engine I found that there was quite a taper developing (can be seen in the pictures, 4.5 -5mm diameter in 50mm ) so I wondered if I had got something else out of true when I rebuilt the headstock.

The first check was the put a length of 10mm silver steel in a collet and check the run out at the far end ~200mm. Better than 0.02mm TIR so at least everything was concentric.

Next check clamp the DTI in the tool post at centre height and run it up and down. Total variation was less than + 0.02mm so the headstock is still parallel to the bed.

Final check. Slide the silver steel back into the collet, centre drill, then bring it back out to 200mm and try it against a centre in the tailstock. Visibly out of line, the bar would deflect as the centre was bought in. When I tried to realign the tail stock there was obviously a problem. My version of the lathe has two clamping screw for the sideways movement and they were obviously fighting against each other. When I took it all apart the critical bearing surface was up to the usual standard with a large chatter mark at one end. That will need some careful attention tomorrow to try and get some sensible adjustment without putting the tailstock barrel out of parallel with the bed.
Best regards

Roger

Offline steamer

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Re: Frustrating Day
« Reply #14 on: December 27, 2013, 10:44:28 PM »
Opposing screws is very common...even on heavy iron

Loose fit on the guiding tongue is not good though.

Tell me that's a good "wring it on" fit...which it should be...if not, we'll have to figure out a way to make it so.

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline Johnb

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Re: Frustrating Day
« Reply #15 on: December 27, 2013, 10:53:43 PM »
When checking the alignment of the tailstock I have always used a test bar mounted between centres. This test bar has two large collars, one near each end. The bar is long enough that I can take a cut on each collar just by moving the saddle along the bed and with the tailstock near the end of the bed. I then mount a tool in the toolpost and take a cut over the collar nearest the tailstock. Then, without adjusting the tool's position relative to the lathe centreline, I move the saddle along the bed and take a cut over the collar nearest the headstock. I then mike up the two collars, they should be exactly the same diameter. If the collar at the tailstock end is larger then the one at the headstock, then the tailstock is displaced towards the back of the lathe bed. If the collar at the tailstock end is smaller than that at the headstock end, then the tailstock is displaced towards the front of the lathe bed. Adjust the sideways position of the tailstock and repeat the cut and repeat until the two collar diameters are the same.

It always takes me two or three tries as I can never remember which way to adjust the tailstock. Maybe next time I do it I'll put an indicator on he tailstock barrel before I adjust. That might help.

John
John Browning. Member of Ickenham and District SME

Offline steamer

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Re: Frustrating Day
« Reply #16 on: December 27, 2013, 11:24:53 PM »
Right Jon....but I'm concerned about a possible condition that I have heard about before with some of the Import lathes.   The Tailstock chuck should be mounted on a "Tennon" like most lathes, except some of the imports have very loose fitting tennons...and as a result they will get out of alignment "suddenly" ....I can't confirm or deny this is the case here...at least not yet.

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline Roger B

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Re: Frustrating Day
« Reply #17 on: December 28, 2013, 11:55:16 AM »
Dave, Thank you once again for your help and advice.

The tennon is indeed not a wringing fit but around 0.5mm free play. I assume the idea was that the two screws would hold it square. When everything is assembled the tennon is clamped together by the tailstock clamping bolt.

I have put up pictures of both surfaces blued against a 8mm square ground HSS lathe tool blank and the two blued together.

I could possibly fit the base on my milling slide to true it up but I think that the body will be too big.
Best regards

Roger

Offline steamer

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Re: Frustrating Day
« Reply #18 on: December 28, 2013, 04:29:56 PM »
0.5mm.....  0.020" Clearance!.... :hellno:


Well!...we will need a plan for this, as the alignment of the tailstock is integral to the fit of the tennon!   You'll chase your tail aligning this forever, until this is fixed. And it won't drill holes worth a )@U)@ without that quill being parallel.   

I am thinking lets be pragmatic here, and we may need to put in a shim, with some adhesive, to bring the fit back to where it needs to be.

Can you measure the female side of the tennon for parallelism?....like really carefully....a good adjustable parallel does wonders in this situation.

Second, put a dial indicator on your cross slide on the end of an arm, and with the tailstock lower shoe, sitting on the ways, how parallel is the front side of the male tennon to the axis of the cross slide? 

Dave

We'll figure something out.

Dave


"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline Roger B

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Re: Frustrating Day
« Reply #19 on: December 28, 2013, 09:04:22 PM »
The female tennon is about 0.2 mm out of parallel and the 'critical' faces are not flat nor vertical.

I put the base on my surface plate with a piece of 10mm silver steel in the V grove and some packing the other side to get it level. Using large and small V blocks I could check the front of the male tennon. At the bottom it appeared to be at 90° to the silver steel rod, but there was at least .05mm (2 thou) gap so that is not vertical.

My first thoughts:

Mount the base on the milling slide with a 10mm rod in the V groove as above, set the rod vertical against the crossslide and lightly mill both sides true.

Work out how to clamp the body onto the vertical slide and set the quill vertical (needs some thought but I think that it may be possible). Lightly mill both sides true.

Put it all back together and check if the quill is parallel to the bed (dial indicator on the carriage).

If good cheer! If not work out how I need to tilt the surface on the body to get it true (much easier now because the surface is flat, smooth and level).

Measure the resultant gap and make a brass shim to fit the gap quite tightly. Replace the clamping screws with some better quality grub screws.

Currently I'm not sure if I can make it worse  :headscratch:
Best regards

Roger

Offline steamer

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Re: Frustrating Day
« Reply #20 on: December 28, 2013, 11:19:17 PM »
Well!    That does well and truly S(*@(*@!.....I'm thinking the plant to make the male tennon flat square and parallel...is a good start.  You will have to decide if the set up is up to the task....sounds a bit optimistic...but I've seen worse.

I'm wondering above the female side.     I assume you only have the lathe that your trying to fix....correct?

If you can mount the tailstock on a knee mounted to the cross slide, you could possibly mill the slot flat square and parallel....if you can set that up, you can then come up with a shim you can bond in place, on the back side of the tennon.   YUCK!....this is not going to be pleasant!...... :o :censored:

OK....lets start noodling......



Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline Roger B

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Re: Frustrating Day
« Reply #21 on: December 29, 2013, 07:37:12 PM »
Family ski day today at Hoch Ybrig (Hi Fabian I waved on the way through) so nothing done on the lathe. It is my only one so I will have to set something up on it (unless I admit total defeat and take the bits into the toolroom at work or wait until I increase my workshop in January). I'll see what I can do tomorrow.
Best regards

Roger

Offline Roger B

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Re: Frustrating Day
« Reply #22 on: December 30, 2013, 04:27:28 PM »
A couple of pictures of Saturday's alignment checks.
Best regards

Roger

Offline Roger B

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Re: Frustrating Day
« Reply #23 on: December 30, 2013, 05:04:46 PM »
Having had a few trials I decided I could hold the parts on the vertical slide and have a chance of keeping the alignment.

First I clamped the piece of 10mm SS to the table and set it vertical against the bed. The base piece was then clamped with suitable packing to get it level and the face of the tenon was checked with the DTI. It was + 0.02mm on the smoothest part. Enough was milled off both faces to get a smooth surface.

Clamping the body was not so easy (gravity is not your friend on a vertical slide). I fitted a stop to rest it on whilst I clamped the top, them removed the stop and clamped the bottom. The bottom face of the body was set parallel to the chuck register and the quill was clocked level to ~0.02mm. Again enough was milled off to get smooth surfaces.

The tailstock was then reassembled using the original clamping screws with no sign of rocking and the quill was checked for parallel to the bed. This was within 0.03mm which I felt was ok at this point.

The gap between the tennon faces was 1.2mm (measured using drill bit shanks) so I milled a piece of 2mm brass down to 1.2mm. When all was back together the tennon would slide with no detectable play  :whoohoo: and the quill was parallel to 0.03 mm horizontally and vertically.

As a final check I put the centre drilled 10 mm bar back in and checked to see how much it deflected as the centre entered the centre hole with the quill retracted and extended. Horizontally this was around 0.02mm (about the same as the runout on the bar)  :pinkelephant: . Vertically the end of the bar was lifted around 0.05mm with the quill extended and retracted so it looks like everthing is true but the complete tailstock is a little too high.

I think that I can live with that, so back to making engines  :cartwheel:
« Last Edit: December 30, 2013, 08:15:54 PM by Roger B »
Best regards

Roger

Offline Roger B

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Re: Frustrating Day
« Reply #24 on: December 30, 2013, 05:41:58 PM »
I've been having problems getting the pictures up.
Best regards

Roger

Offline Roger B

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Re: Frustrating Day
« Reply #25 on: December 30, 2013, 05:44:15 PM »
Another try
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Roger

Offline Roger B

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Re: Frustrating Day
« Reply #26 on: December 30, 2013, 05:45:25 PM »
And the rest
Best regards

Roger

Offline smfr

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Re: Frustrating Day
« Reply #27 on: December 30, 2013, 06:23:15 PM »
Looks like a good result, Roger!  :ThumbsUp: :ThumbsUp:

Simon

Offline steamer

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Re: Frustrating Day
« Reply #28 on: December 30, 2013, 06:34:01 PM »
A braver man than I Roger!.....Congrats! :praise2: :praise2:


Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline Roger B

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Re: Frustrating Day
« Reply #29 on: December 30, 2013, 07:23:51 PM »
Not so brave, I started fiddling with the knowledge that I can get a replacement tailstock with lever locking for £80 from ARC Eurotrade. That would probably also require some furkling (old English engineering term) but I couldn't actually do irreversible damage (and would certainly learn some stuff on the way).
Best regards

Roger

Offline Roger B

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Re: Frustrating Day
« Reply #30 on: December 30, 2013, 07:26:44 PM »
A final thought  :noidea:  How come that for all the important checks the DTI was facing the wall or the floor  ::)
Best regards

Roger

Offline steamer

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Re: Frustrating Day
« Reply #31 on: December 30, 2013, 08:17:49 PM »
I suspect you wanted the extra challenge........ 8)


Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline Graham Meek

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Re: Frustrating Day
« Reply #32 on: December 31, 2013, 11:09:34 AM »
Hi Roger,

Looks like you have had a challenging time, I too did some repairs to a Mini-Lathe back in May, a chap was having difficulties on the ME Forum and in the end after he had got so frustrated trying to sort it out I suggested he bring the lathe over, (about a 4-5 Hour round trip).

The photographs on the link below show the extent of the work required,

http://www.model-engineer.co.uk/albums/member_album.asp?a=26835

There were no dovetails with the correct angle, all the "ways" on the carriage, cross-slide and top-slide had been attacked with an angle grinder and the gibs were that thin you could pull the cross-slide off the carriage. If I tell you that this lathe was purchased new it will dispel any ideas that someone else other than the manufacturer had visited this machine.

During the week or so that it took me to rectify this machine it came out in the emails that we exchanged that his brother had purchased a lathe at the same time, well when the lathe was ready for collection his brother's lathe was left behind for me to work on and yes it was in exactly the same condition.

My best regards
Gray,

Offline Roger B

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Re: Frustrating Day
« Reply #33 on: December 31, 2013, 04:15:55 PM »
Hi Gray,

This lathe actually isn't so bad. I've had it for quite a while and managed to make an engine that runs (just). This one isn't a Seig and had a few advantages such as there was already a cover on the back of the apron gears and the leadscrew is extended through the right hand bearing so it is easy to fit a handwheel for milling.

I think a lot of the problems appeared when I started putting lumps of 50mm CI in it  ::)
Best regards

Roger

Offline Graham Meek

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Re: Frustrating Day
« Reply #34 on: December 31, 2013, 05:39:09 PM »
Hi Roger,

The two lathes that I repaired were not Sieg either, I had chance to borrow a Sieg lathe when I was designing a version of my screwcutting clutch to fit this lathe, they are quite well made I found. I also designed a Handwheel dial with a zero-able Dial to fit this lathe while I had it. The dials read 0-1" or 0-25 mm if you prefer, both these attachments are due to be published in the New Year.

I have attached a couple of photographs of both items.

My best regards
Gray,

Offline Roger B

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Re: Frustrating Day
« Reply #35 on: January 01, 2014, 07:04:33 PM »
Hi Gray,

Thank you for those pictures. I will probably not do much more to this lathe. I am in the process of buying a slightly smaller but rather better quality and nicely equipped lathe. As both are liftable I will be able to keep this one under the shelves for when I do need slightly more capacity. The new engine will have  a 125mm flywheel which is at or beyond the limit for the new one.

Wishing you all the best for the New Year
Best regards

Roger

 

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