Swing over bed limitation for flywheels

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Swing over bed limitation for flywheels

This topic has 23 replies, 15 voices, and was last updated 4 September 2025 at 11:54 by Engine Builder.

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1 September 2025 at 18:03 #814788
Steve Huckins
Participant
@stevehuckins53362
Following my previous query regarding holding various parts in a 100 mm chuck, I am now better equipped to deal with anything likely to arise in future now. ( famous last words ! ) Thanks to everyone again for the education.

I have only made stationary engines and have found my choices so far to have comfortably fitted my SC4 lathe. Also my VM25 mill with 3 axis DRO gives great service.

But I was wondering how on earth would I ever be able to try something larger that had a fly wheel bigger than 810 mm diameter as this is the swing over the bed of this lathe ? Is there a service which will machine a fly wheel for those in a position like me ?

I think there are quite a few other casting kits I could and would like to make apart from the fly wheels. Eg the Blackgates Steeple Engine or Reeves Vulcan Beam Engine. All of which I like the look of.

Anyone have the same problem or any solutions ?

Thanks as always

Steve
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1 September 2025 at 18:12 #814793
JasonB
Moderator
@jasonb
Your SC-4 should be able to swing 210mm not 180mm (the SC2 & 3 are 180mm)

But anything larger would need a bigger lathe. There are sometimes adverts in ME&W for machining services or asking on the forum may find a member willing to do it for some pocket money. Early on in my model making journey I found the 200mm swing of my lathe would not cope with the typical 9″ flywheels of many models but found a guy in ME who turned it for me.
1 September 2025 at 18:28 #814803
Steve Huckins
Participant
@stevehuckins53362
Yes quite right Jason but I’m sure I mentioned 210 mm not 180 mm. Not that it matters though. The overall problem is still relevant.

I guessed your reply may be my only options. Of course it would be nice to have space and pocket money for a larger lathe but hopefully I can post as you suggest and hope a kind and generous kindred spirit pops up. I still have a couple of casting kits to keep me occupied for quite a while and will undoubtedly move up a size following those.

Steve
1 September 2025 at 18:31 #814804
not done it yet
Participant
@notdoneityet
810mm is quite large but could possibly be easily machined on a reasonably sized milling machine using a rotary table – but not on your lathe!
1 September 2025 at 18:41 #814808
Martin Connelly
Participant
@martinconnelly55370
Pretty sure the 810mm is a typo and should be 210mm. Jason read it as a typo of 180mm. However your option of using a mill and RT to machine a larger diameter than will fit a lathe is a possible solution but you would have to take care to keep the cutting forces low enough to ensure the RT drive gear is not damaged. The cheaper ones can have poor engagement and weak materials. Maybe a very large swing boring head type of arrangement would be a better option if you can make yourself a suitable tool.

Martin C
1 September 2025 at 18:56 #814811
Steve Huckins
Participant
@stevehuckins53362
More apologies. Yes I should really have said 210mm not 810mm or anything else.

I think I had 8 inches or so imperial in my head as I still can picture sizes in imperial out of long habit.

Steve
1 September 2025 at 20:10 #814829
Stuart Smith 5
Participant
@stuartsmith5
Steve

You could join a model engineering club. A lot of clubs have a workshop with possibly a larger lathe.

Stuart
1 September 2025 at 20:48 #814833
Julie Ann
Participant
@julieann
Use a horizontal mill with the work mounted on the spindle and the tool on the table, like a facing lathe. I can swing 19″ in the gap on my lathe but on the horizontal mill could do double that.

Julie
1 September 2025 at 20:50 #814835
Bazyle
Participant
@bazyle
On an SC4 things would perhaps get difficult above 400mm radius (that’s 16 inches). Make a spigot to match the bore of the flywheel you have prepared and reamed (we can discuss that later if necessary but a nice exercise for the reader).
Mount spigot on the cross slide in line with bore of spindle (remove tailstock on larger wheels.
Spin a flycutter in the lathe while rotating the flywheel by hand. To get better rotational control attach a long lever if necessary. If you think hard you can work out how to get a slight convex surface on the rim for flat belt retention. To do the edges of the rim lock the spindle and use a 4-jaw to hold a lathe tool at the right position.

It is helpful to have your drilling machine on the right of your lathe. Then you can use it to drive a pulley (child’s bicycle wheel) attached to a flywheel mounted on the aforementioned spigot while machining with tool in the 4-jaw.

Similar things can be done on the mill but you may be more limited by the throat depth and table size. Use the pulley concept to protect the rotab gear.
2 September 2025 at 07:11 #814853
JasonB
Moderator
@jasonb
On the few occasions where I have held a flywheel by the bore and attempted to turn the rim the results have never been that good, the initial interrupted cuts see the work deflecting away from the tool and finish cuts suffer from fine chatter marks. I would imaging swinging it on a less rigid hobby mill or rotating manually would give even more issues. Like wise the typical hobby rotary tables can have too much backlash which shows more the further from the ctr you are machining.

I have also seen all the spokes fail on a iron flywheel being held by its hub to machine the rim, not even a large one just 125mm dia but the spokes were quite delicate. If I can find the photo which was sent to me I’ll post it later.

I’ll say it again the SC-4 will swing 210mm (105mm radius) so a 8″ flywheel would probably be the limit as a casting will be larger than finished OD
2 September 2025 at 09:50 #814859
noel shelley
Participant
@noelshelley55608
Although a Myford is known as the “7” There is a 9″ or 230mm face plate that can be swung in the gap. Old hands will know this, but many may not. Noel.
2 September 2025 at 10:14 #814862
JasonB
Moderator
@jasonb
Which is the reason that so many of the older legacy stationary engine kits tend to have flywheels around the 9″ dia mark as they could be swing in the Myford’s gap.

Depending on what takes your fancy any of the designs can be scaled down (or up) if you don’t mind a bit of fabrication or cutting from solid. Just pic a ratio that is based on the largest dia you can comfortably swing and adjust everything to suit.

On the Vulcan you may even get away with making a flywheel 20mm smaller from 8″ thick wall tube without it looking out of place. Steeple engine is a fairly straightforward one to fabricate but would need making at 80% of the drawing size.
2 September 2025 at 10:57 #814870
Roderick Jenkins
Participant
@roderickjenkins93242
In days gone bye when new large Chinese lathes and ex-industry old British iron weren’t readily available, one of the options was to bolt a second headstock to the bed that was driven by the lathe spindle:

Image from Lathes.co.uk

A suitable riser for the tool was also required.

Rod
2 September 2025 at 13:25 #814901
cogdobbler
Participant
@cogdobbler
On 2 September 2025 at 09:50 noel shelley Said:

Although a Myford is known as the “7” There is a 9″ or 230mm face plate that can be swung in the gap. Old hands will know this, but many may not. Noel.

Which is why the Vulcan Beam Engine flywheel mentioned in the OP is 8.75″ diameter! Or 222mm. Just outside the SC4’s 210mm capacity.

A 12mm packing piece between bed and headstock might do the job? Two strips could be laid along the inverted V way perhaps?

Would it be sacrilege to cut a 10mm deep gap into the SC4 bed to partially “Myfordise” it? Would the bed casting be stout enough to remain rigid?
2 September 2025 at 13:34 #814903
JasonB
Moderator
@jasonb
Looking at the build articles for the Vulcan it was said that provided the casting was reasonable then the rim did not need to be turned. In which case it could be spun horizontally in the mill if you did want to tart up the profile a bit before painting. It’s a round section rim.
2 September 2025 at 14:32 #814918
Georg49
Participant
@georg49
TS-Modelldampfmaschinen in Germany offers a completely machined 220mm flywheel (“Schwungrad 220 bearbeitet”). When ordering you specify the required diameter of the axlehole.

Georg49
2 September 2025 at 14:41 #814920
Steve Huckins
Participant
@stevehuckins53362
I like the idea that the Vulcan flywheel may only need a small amount of work and not necessarily in the lathe.

I think for all other options I will probably ask for help.

I am on Exmoor and try as I might, there are no ME clubs within distance of home. That’s why I am so grateful for this forum.

cheers

Steve
2 September 2025 at 14:52 #814921
Howard Lewis
Participant
@howardlewis46836
Not applicable to a SC4, in this case, but have faced and turned brake discs down to 11″, in the gap of a Myford ML7.

Howard
2 September 2025 at 15:13 #814925
Bazyle
Participant
@bazyle
On 2 September 2025 at 14:41 Steve Huckins Said:

I am on Exmoor and try as I might, there are no ME clubs within distance of home. That’s why I am so grateful for this forum.

cheers

Steve

Come down to Exeter DMES on Sunday 7th as we are having a model show at St Katherine’s Priory as well as the usual public running and Junction 73 model railway open. See the new viaduct and ask one of the committee to show you the big Colchester to measure its capacity. There are workshop days on Tuesday evenings. It is right next to Morrisons so you can do some shopping too.

Also although there is a club around Barnstaple but without premises. (search this site for rare inputs). Check that and the Men’s Sheds as some members have machinery. Last month I was helping bore one back wheel of the OMIS entry for the Bideford Soapbox Darby (see youtube for stream) that was over 10 in dia.
2 September 2025 at 21:03 #814954
Wade Beatty
Participant
@wadebeatty78296
Julie’s comment about mounting on the horizontal arbor made me take a second look at these wheels which are offered cheap
2 September 2025 at 21:04 #814956
Ian P
Participant
@ianp
On 2 September 2025 at 10:57 Roderick Jenkins Said:

In days gone bye when new large Chinese lathes and ex-industry old British iron weren’t readily available, one of the options was to bolt a second headstock to the bed that was driven by the lathe spindle:

Image from Lathes.co.uk

A suitable riser for the tool was also required.

Rod

Been there, and have the Tee shirt!

This is a 5″ Boxford temporarily modified to machine a 12″ diameter aluminium part. I was fortunate in that at the time I needed to manufacture (an end cap for underwater camera housing) I had a spare headstock off a 4.5″ model A

The headstock is packed up on on some 1″ square MS barstock, not visible in this picture is a (second) motor on a bracket hidden behind the headstock. I used the lathes power cross feed to do the facing.

Ian P
3 September 2025 at 21:25 #815067
Engine Builder
Participant
@enginebuilder
I made this for my ML10 and can turn 12″ flywheels now!
4 September 2025 at 11:44 #815127
cogdobbler
Participant
@cogdobbler
On 3 September 2025 at 21:25 Engine Builder Said:

I made this for my ML10 and can turn 12″ flywheels now!

Nice! Where did you get the casting?
4 September 2025 at 11:54 #815131
Engine Builder
Participant
@enginebuilder
Nice! Where did you get the casting?

I made my own castings.

Sadly i don’t have the pattern anymore so cannot offer it to others.

I had a big clean out of all the patterns i had made and never thought anyone would want on of these.

David
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