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What have I done wrong??

5inch Simplex wheels

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David Fox 328/10/2017 08:03:20
9 forum posts

The six wheel on the Simplex shouldn't be too difficult surely? I am fairly new to model engineering but thought this should not throw up any great problems. I mounted each of the castings on a 4 jaw independent chuck and faced the back of each. Then whilst still in the chuck centre drilled then drilled through with a 1/2inch drill. Then bored it out to just under 11/16" and finished off each with a 11/16" hand reamer.

I had bought a 3mt soft end 40mm x 40mm arbour which I turned down 15mm of which to be a tight fit on the newly bored and reamed wheels leaving a shoulder to support the back of each wheel. I then tapped an M8 thread in the end of the arbor so a bolt could then hold each wheel firmly in place.

On trying the wheels on the arbor they fitted perfectly sliding on tightly with a little friction but on running the lathe the rim of each wheel moves from side to side by about 2mm when firmly against the shoulder! WHY? What have I done wrong?

 

2

The lathe is a Seig SC4 about 8 years old but not at all heavily used. The wheels cast iron and the 3 mt stub bought recently from the midlands model engineering exhibition.

Any help gratefully received!

 

Dave F

 

Edited By JasonB on 28/10/2017 08:19:03

JasonB28/10/2017 08:20:04
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How did you do the reaming? hand held or using the tailstock for support?

David Fox 328/10/2017 08:31:32
9 forum posts

Hand held. But all the wheels are exactly the same.

Michael Gilligan28/10/2017 08:43:06
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Posted by David Fox 3 on 28/10/2017 08:31:32:

Hand held. But all the wheels are exactly the same.

.

In that case; logic suggests that the 4-jaw is mis-aligned

Have you checked that the faces of the jaws are actually level ?

MichaelG.

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[quote] I mounted each of the castings on a 4 jaw independent chuck and faced the back of each. Then whilst still in the chuck ...  [/quote]

Edited By Michael Gilligan on 28/10/2017 08:45:12

David Fox 328/10/2017 08:46:18
9 forum posts

That's what I would have thought but surely if that were the case the rear face of the wheel would be slightly off or am I making assumptions here?

David George 128/10/2017 08:47:56
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Hi when you machine castings you release stresses and when you undo the four jaw chuck the casting springs slightly. I would have skimmed both sides before finishing the bore.

David

Chris Evans 628/10/2017 08:52:34
1587 forum posts

All is not lost. There should be enough metal in the bores to true up to 18mm after all you are making both parts so can use whatever size you want.

David Fox 328/10/2017 08:52:53
9 forum posts

Thanks it certainly seems to have released some stresses. But mine have gone through the roof. Bizarre!

David Fox 328/10/2017 08:54:33
9 forum posts
Posted by Chris Evans 6 on 28/10/2017 08:52:34:

All is not lost. There should be enough metal in the bores to true up to 18mm after all you are making both parts so can use whatever size you want.

Thanks. I think this will have to be the way forward!

JasonB28/10/2017 08:58:13
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Has the mandrel that you made been removed and refitted to the lathe between making it and mounting the wheels. If it was not seated right when machined or ha snot gone back in the same then that would give a constant error on the wheels.

Is there a slight radius on your mandrel where the spigot meets the flat face, often left by an insert tip, if you the edge of the holes needs to be chamfered/CSK to clear that and allow the wheel to sit down flat

I would have thought movement in the castings would not be the same for all wheels. Easily checked by placing the machined face on a flat surface and see if it is shaped like a Pringle.

Also not sure chuck jaws would cause the issue as the surface and bore would be true to each other as machined at one setting no matter how wonky the wheel was mounted.

You could check the bore is true to the machined face by turning the end of a bar to a good push fit in the 11/16" hole and then without removing from the lathe push on a wheel and see if it runs true.

Edited By JasonB on 28/10/2017 09:01:02

Chris Evans 628/10/2017 09:02:01
1587 forum posts

Good thoughts Jason, I tend to undercut this type of mandrel out of habit to get a good seating from the mating part.

David Fox 328/10/2017 09:11:25
9 forum posts
Posted by JasonB on 28/10/2017 08:58:13:

Has the mandrel that you made been removed and refitted to the lathe between making it and mounting the wheels. If it was not seated right when machined or ha snot gone back in the same then that would give a constant error on the wheels.

Is there a slight radius on your mandrel where the spigot meets the flat face, often left by an insert tip, if you the edge of the holes needs to be chamfered/CSK to clear that and allow the wheel to sit down flat

I would have thought movement in the castings would not be the same for all wheels. Easily checked by placing the machined face on a flat surface and see if it is shaped like a Pringle.

Also not sure chuck jaws would cause the issue as the surface and bore would be true to each other as machined at one setting no matter how wonky the wheel was mounted.

You could check the bore is true to the machined face by turning the end of a bar to a good push fit in the 11/16" hole and then without removing from the lathe push on a wheel and see if it runs true.

Great thoughts. Will report back in a couple of hours when I've been in the workshop. I did use an insert tip but. Cut slightly further and use its side face to give a slight inner taper on the mandrels side thus avoiding that small radius if you get my thoughts!!

MichaelR28/10/2017 09:44:11
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It's good to see how others go about doing the same job, Simplex wheels on this forum Here Mike.

duncan webster28/10/2017 10:42:45
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I've never been over impressed with this method of machining wheels. I have 2 alternatives

  1. wheels in 4 jaw skim across what will be the inner face and bore a slight recesss at the outer end of the spokes. Then turn round and grip by this recess. Adjust to get the rim running true radially, face, turn outside diameter and bore for axles. It must be concentric, it's all been done at one setting
  2. wheels in 4 jaw, skim across what will be the inner face. Bolt some packing to faceplate slightly smaller than wheel OD using csunk screws, face off. Bolt wheels to faceplate, proceed as above. You need to put some suitable holes in the packing first to clear the bolts holding the wheels down

The second way is easier. For smaller wheels I make a faceplate by drilling and tapping 2 holes in a suitable bit of bar, then mount in chuck, face off in situ. This means you can have the wheels securing bolts anywhere you want not dictated by faceplate. I don't use a reamer (too mean to buy one) just bore to size and make axles to suit. David can recover his wheels by using method 2 and clocking the OD to run true before reboring axle holes by as little is needed to true them up.

Edited By duncan webster on 28/10/2017 10:43:26

Edited By duncan webster on 28/10/2017 10:50:07

OuBallie28/10/2017 10:44:30
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1149 forum posts
661 photos

Did you clean the spindle bore before inserting the mandrel?

Geoff - Put the Marlow to good use yesterday.

Andrew Johnston28/10/2017 11:27:12
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5188 forum posts
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I'd put my money on the reaming being the cause. Using a hand reamer without guidance isn't going to create an accurately aligned hole. I'm with Duncan I'd have bored to size against a home made gauge. If I had an 11/16" machine reamer I might have used it, but I haven't got one.

Andrew

Bob Rodgerson28/10/2017 12:18:16
585 forum posts
166 photos

I tend to agree with Andrew, hand reaming without a guide is prone to problems. I always try to use a centre held in the tailstock to hold it true while holding the reamer with an adjustable spanner or tap wrench if it will fit on the flats on the end of the reamer while advancing the tailstock. It's a bit od a juggling act but it gets results.

However for really Concentrically accurate work nothing beats working with a go nogo gauge or a pre-prepared mandrel of the desired size and boring to suit.

Michael Gilligan28/10/2017 13:58:23
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Posted by David Fox 3 on 28/10/2017 08:31:32:

Hand held. But all the wheels are exactly the same.

.

Note: For my 'analysis', I was relying relying upon this statement ^^^ being true [at least to within the capability of David's instruments and technique] ... Presumably, any of the other explanations offered would result in measurable differences between the individual wheels.

MichaelG. dont know

Mick B128/10/2017 14:44:49
1433 forum posts
77 photos

Maybe it's how I'm reading it, but I can't see how this would occur except by eccentricity of the initial 4-jaw setting.

Why wouldn't you use the reverse jaws on your 3-jaw to face the rear, and bore for the axle? It's only going to be a couple of thou out, and you can clean that up when you mount on the mandrel. Or is the periphery of the casting too rough?

Ian S C28/10/2017 15:19:40
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7468 forum posts
230 photos

A hand reamer generally has a centre hole each end, when reaming a hole in a piece machined in the lathe, leave the piece in the lathe take the reamer and back it up with the tail stock centre, and as you turn the reamer/ or the chuck (I don't use power for this), wind the tail stock in, keeping pressure on the reamer. Cast Iron, no lubricant, steel lubricate, I just use engine oil.

Ian S C

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