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Davek0974
01-27-2009, 04:10 PM
Hi all,

I am seeking advice on a small problem, here's the scenario...

I have a Bridgeport 9x48 varispeed, and a Colchester Student lathe.
I need to machine a 6" radius into the bottom of a traction engine cylinder block so it sits on the boiler. Length of block is about 7". I have a 2" R8 boring head.

Whats the best way of doing the job on the given equipment? I dont mind making new tools or attachments etc or getting hold of the right stuff if needed. I know the length is beyond the quill travel but i could lift the knee i guess.

Material is good quality cast iron.

Anyone got any ideas?

As usual, all ideas are much appreciated.

Dave

tony ennis
01-27-2009, 04:22 PM
Do you have a band saw?


but i could lift the knee i guess.

Or go at it from both sides.

aboard_epsilon
01-27-2009, 04:31 PM
so the boiler is 12 inch diameter and the cylinder sits on it horizontally.

i would take as much off with an endmill..with it horizontal on the milling machine
then make a big fly cutter about five inches in diameter, to take the rest off with it vertical on the milling machine..will take many many passes.

all the best.markj

SGW
01-27-2009, 04:38 PM
One way to do it would be to figure out incremental depth steps and get it close that way, then finish with files.

That is, clamp the block down flat on the table. Locate the centerline. Put say, a 1/4" dia. end mill in the spindle. Figure out what the depth needs to be for a given Y offset so the corner of the end mill *just* goes deep enough to touch the desired final radius. This will be symmetric across the centerline. You'll end up with a series of small steps, but depending on your patience and how small your Y increments are the ridges that get left can be pretty small.

Just Bob Again
01-27-2009, 04:44 PM
Why machine a full-contact surface? Not likely to be a perfect cylinder anyway. Make 3 ribs that contact the boiler, center and two edges. Use CAD to figure the depth, relieve the non-contact areas stepwise. Use the largest radius ball mill you can find. If you want the ribs to contact better, simply stick some SiC sandpaper onto the boiler with tape and rub it back & forth a bit. If it were a heavy item, I'd do otherwise but this is the easy way.

John Stevenson
01-27-2009, 04:45 PM
Dave,
Not got time to work out the maths, hopefully someone else will chime in but it can be done easily with a flycutter set in the boring head and the head of the Bridgy tilted.

Think about this, with the head vertical the tool describes a radius of infinity on the work, i.e. flat. in the horizontal position the radius is equal to the tool radius.

From horizontal to vertical the radius will go from R to infinity so it's
possible to cut a radius larger than the tool radii

A couple of pictures that may show the principle is the following one of radiusing the back of a rack so it can lie on a tubular column.

http://www.stevenson-engineers.co.uk/files/rack3.jpg



http://www.stevenson-engineers.co.uk/files/rack4.jpg



[edit] from reading some of the other posts, this radius needs to be a good fit on the boiler as it's a steam fit face .

Davek0974
01-27-2009, 04:49 PM
Why machine a full-contact surface? Not likely to be a perfect cylinder anyway. Make 3 ribs that contact the boiler, center and two edges. Use CAD to figure the depth, relieve the non-contact areas stepwise. Use the largest radius ball mill you can find. If you want the ribs to contact better, simply stick some SiC sandpaper onto the boiler with tape and rub it back & forth a bit. If it were a heavy item, I'd do otherwise but this is the easy way.

I see where your'e coming from but it needs to be a steam tight joint to 180psi. There is a gasket but only a thin one.

I think the large flycutter is the best option and was top of my 'possibles' list. Something like a bar welded to an R8 arbour with a tipped tool in it?

The curve is already cast in roughly, i just need to remove about 3mm of allowance to give a good fit on the boiler.

Dave

Davek0974
01-27-2009, 04:52 PM
Dave,
Not got time to work out the maths, hopefully someone else will chime in but it can be done easily with a flycutter set in the boring head and the head of the Bridgy tilted.

Think about this, with the head vertical the tool describes a radius of infinity on the work, i.e. flat. in the horizontal position the radius is equal to the tool radius.

From horizontal to vertical the radius will go from R to infinity so it's
possible to cut a radius larger than the tool radii

A couple of pictures that may show the principle is the following one of radiusing the back of a rack so it can lie on a tubular column.

http://www.stevenson-engineers.co.uk/files/rack3.jpg



http://www.stevenson-engineers.co.uk/files/rack4.jpg



[edit] from reading some of the other posts, this radius needs to be a good fit on the boiler as it's a steam fit face .

I like the theory of that, where would i look for the angles and tool radius etc, i've never seen that in a book or anywhere else come to think of it?

Thanks
Dave

Evan
01-27-2009, 04:58 PM
Keep in mind thaqt the technique John suggests won't make a true circular cut but instead an elliptical cut. The side projection of a tilted circle is an ellipse so for a particular desired depth of cut the edges will be too high/low. The amount of error is dependent on the ratio of the fly cutter size to the desired radius and the depth of cut. The closer the fly cutter is to the actual diameter of cut and the shallower the cut the less error in the shape.

aboard_epsilon
01-27-2009, 05:09 PM
Keep in mind thaqt the technique John suggests won't make a true circular cut but instead an elliptical cut. The side projection of a tilted circle is an ellipse so for a particular desired depth of cut the edges will be too high/low. The amount of error is dependent on the ratio of the fly cutter size to the desired radius and the depth of cut. The closer the fly cutter is to the actual diameter of cut and the shallower the cut the less error in the shape.

hmmm dunno

just imagine you slice off a bar at 45 degrees ....that slice will fit inside a tube and block it at 45 degrees ...like throttle butterfly.

so johns flycutter is following path of circle ..

then again i could be wrong ..its very hard to imagine without actually doing it .

all the best.markj

Evan
01-27-2009, 05:12 PM
To see the shape produced draw a circle of the same diameter of the fly cutter or boring head and then scale it in the vertical axis so the minor diameter is the same as two times the depth of cut.

Here are examples of the shape made as you move from horizontal to vertical.

http://metalshopborealis.ca/pics/section.gif

Peter S
01-27-2009, 05:23 PM
Dave,

Bridgeport boring heads like mine have a horizontal hole for a boring bar, as well as the vertical holes, in other words you can fit tooling to bore any radius. Great because you can adjust the radius in the normal way. Maybe your one doesn't...

I have used a large capacity fly cutter on a BP - it was a piece of flat bar, say 50mm x 15-20mm flat bar, about 300mm long, drilled in the middle to attach to an R8 arbor, and made to take a piece of HHS toolsteel on the end. (Intended for very light clean-up work on aluminum plates etc). Downside is no radius adjustment, so how about making something to fit your boring head so you get the benefits of adjustment? Could be double-ended for balance as well?

barts
01-27-2009, 05:33 PM
If I read the specs right, that lathe of yours will handle 13" or so diameter... so can you make a suitable boring bar to run between centers, and bolt the cylinder to a bracket of some sort bolted to the top slide (compound removed...)? This would be much stronger than than the BP, I think.

- Bart

shadoof
01-27-2009, 06:24 PM
Hi, could you hold the block on a face plate and machine the radius in like this,

http://i156.photobucket.com/albums/t20/shedfull_2007/profileturninggeneration.jpg

http://i156.photobucket.com/albums/t20/shedfull_2007/profileturninggeneration001.jpg

http://i156.photobucket.com/albums/t20/shedfull_2007/profileturninggeneration002.jpg


Lee.

Davek0974
01-28-2009, 03:04 AM
Wow! Thanks all,
theres some food for thought there.

I'll look into a custom flycutter, with carbide tips i think. I actually need two radius jobs on this, one at 6" and one at 6.5" so ab bar with a small amount of adjustment will do both.

The boring head does have the cross-hole but its only a 2" head so that will mean a 5" tool, sounds a bit springy to me.

I'll get the thinking cap on.

Dave

Peter S
01-28-2009, 07:30 AM
The boring head does have the cross-hole but its only a 2" head so that will mean a 5" tool, sounds a bit springy to me. Dave

Dave,

The tool doesn't have to be springy. It can be (for example) 25mm diameter mild steel stepped down to fit your cross-hole. A good fit, use as much off the cross hole as you can, might get away with it....Easy to try.

boaterri
01-28-2009, 04:49 PM
Deleted, I was beaten to the reply.

Rick

Mcgyver
01-28-2009, 05:13 PM
it'll be an ellipse, but may be close enough....cylindrical section not perpendicular to the axis is an ellipse. Mark, picture making the cut with a 1/2 endmill at 45 degrees.....the endmill forms a cylinder. Now if we take 1/2" disk and lay it in the groove milled at 45 degree angle, for sure it will find perfectly.... but will it fit if we hold it straight up and down? It can't, because straight up and down is a section of the endmill's cylinder that is not perpendicular to the cylinder, by definition its an ellipse

Mcgyver
01-28-2009, 05:16 PM
OT, that devise you sketched will cut a concave or convex section of a sphere, it will NOT cut a length of a cylinderical curve....

aboard_epsilon
01-28-2009, 05:58 PM
At 45 degrees ...I think ..not sure... the cutter will cut a perfect 90 degrees of a circle...after that it eclipes off.

that's what's in my head ..

all the best.markj

Evan
01-28-2009, 06:08 PM
A cut through a cylinder will only produce a circular section at 90 degrees to the axis. At any other angle it produces an ellipse. At 45 degrees the ellipse will have a major/minor diameter ratio of sqrt(2)/1

John Stevenson
01-28-2009, 06:47 PM
Evan is correct but as Mac has said over a 6" radius the difference may not be noticeable.

On the rack I did it was that narrow it would be very hard to measure.

Bart has probably come up with the best idea of mounting it on the cross slide and using a between centres boring bar although the Student doesn't have tee slots to facilitate holding this.

Dave,
Probably not relevant but if you get stuck you can come up and use my big TOS at anytime if you get anything too big, I think it handles about 30" in the gap

.

Davek0974
01-29-2009, 02:37 PM
Thanks for all the tips guys, and thanks John for the offer of m/c use.

I'm thinking of going with either a cross extension in the boring head or some gizmo made up of an R8 arbor and some bar stock.

My colchester does actually have tee slots on the saddle to each side of the cross slide. I will check the idea of boring on the lathe as well, it would certainly be faster.

Dave

speedy
01-29-2009, 03:29 PM
Swing on the Student is 12" over the bed, 9" over the carriage and 8" over the cross slide.

Davek0974
01-29-2009, 03:57 PM
Swing on the Student is 12" over the bed, 9" over the carriage and 8" over the cross slide.

Yes that would be bit of a problem:)

Im leaning towards mounting it on an angle plate and using the quill/knee.

Dave

Evan
01-29-2009, 04:57 PM
No need to make a large diameter dangerous fly cutter. You can use a small one or the boring head to do it.

Set up a piece of sturdy flat stock to hold the work with a pivot at the right distance. Fix the work to it as shown. Using a regular fly cutter set to cut on the edge and run a cut the length of the work up and down. Index the work over on the pivot and do it again. Because of the relatively large radius of the cutter it won't take many such cuts to produce a circular cut within a few tenths.


As seen from above:

http://metalshopborealis.ca/pics5/jig7.jpg

The flat stock could be a large plate with the vise fixed to it and a pivot point drilled in it.

Peter S
01-29-2009, 05:34 PM
I was watching a film showing locomotive building in the 1930's. The cylinders are cast with a curved saddle on which the boiler sits. This curve was being cut by a modified slotter. I am hazy on the detail, but the radius was achieved by having a bar of the correct length pivoted at one end, and with cutting tool on the other end. The slotting head was connected to this bar, so causing it to arc up and down. Clever, I reckon.

Davek0974
01-30-2009, 05:13 AM
No need to make a large diameter dangerous fly cutter. You can use a small one or the boring head to do it.

Set up a piece of sturdy flat stock to hold the work with a pivot at the right distance. Fix the work to it as shown. Using a regular fly cutter set to cut on the edge and run a cut the length of the work up and down. Index the work over on the pivot and do it again. Because of the relatively large radius of the cutter it won't take many such cuts to produce a circular cut within a few tenths.


As seen from above:

http://metalshopborealis.ca/pics5/jig7.jpg

The flat stock could be a large plate with the vise fixed to it and a pivot point drilled in it.

Thats a thought. I have used that method to cut radius links for stephensons valve gear but it used an endmill and the plate sat ontop of a rotab, the point where the clamp is was driven by the rotab enabling it to effectively turn a much larger radius than the table.

I hadnt thought of using a side cutting tool, it would only need to be slightly bigger than the boring head i guess.

Would a 5-tip side/face mill work??? I have a 65mm one of those.

how about using the rotab to do the same as the links, i.e. instead of making a pass vertically then repositioning, make the pass around the radius and then lower and repeat??

Getting near to a working plan i feel:)

Thanks

Dave

Circlip
01-30-2009, 06:19 AM
Without seeing the drawing for the block Dave, from memory, T E cylinder blocks don't usually have the mounting face vertically in line with the cylinder bore. Conventionally the saddle is normally bored with a between centre boring bar on the lathe. How are you going to bore the Bore??

Regards Ian.

Davek0974
01-30-2009, 07:24 AM
The bore is only 3.5" so i can do that easily on the BP with boring head. Its lined anyway so the finish does not have to be cylinder quality.

Here's a picture of the new cylinder block standing next to my finished smaller engine...

http://www.davekearley.co.uk/Engineering/LittleSamson/LS%20Pictures/sizecomp1.jpg

The top is rough-milled first, then the ends, then its bored out and then the saddle is cut.

Hope that helps a bit.

Dave

Circlip
01-30-2009, 07:54 AM
Yes, but the axis's still have to be square and parallel with each other.

Regards Ian.

Davek0974
01-30-2009, 08:31 AM
On the smaller one, i milled the round flange around the cylinder and the edge of the saddle at one setting for each end, that way i could clamp on the flange to bore the cylinder out and than clamp through the cylinder to machine the saddle knowing that both would be in-line and as square as i could get. It worked well.

My lathe is not big enough to swing the cutter radius needed for the saddle.

Dave

John Stevenson
01-30-2009, 08:52 AM
Dave,
hang fire though of another wau with the Bridgy [ shudder ] but need to do a sketch, so later.

Circlip
01-30-2009, 09:17 AM
You got mail Dave.:D

Providing you do the machining pertaining to the cylinder bore and "Block" first, e-mail should be RELATIVELY easy.

Regards Ian

Duffy
01-30-2009, 11:30 AM
In "The Shop wisdom of Phillip Duclos" there are plans for a 10" fly cutter on an R-8 arbor. Would 12" be out of the question? The one caveat was that the speed had to be LOW. He also stated that he had used it on aluminum, but with the carbide cutters and light cuts, why not?

Evan
01-30-2009, 02:24 PM
Why not? Because it isn't necessary.

John Stevenson
01-30-2009, 02:52 PM
Thinking about this whist working today, yes I know it was painful but one has to do ones best...
Also thinking about what Ian said about keeping everything in plumb

How about this ?

First off machine the valve block face to get a reference surface.
For anyone who doesn't know that's the face on the right hand side of Dave's casting and it's similar to the right hand side of the finished cylinder on the model.

Then using the Bridgy [ shudder ] with the head spun thru 90 degrees and the valve face bolted to some packing rails you can use a long boring bar in the spindle and supported on a travelling plummer block bearing on 'tother end.

Crap sketch.

http://www.stevenson-engineers.co.uk/files/horizontal_boring.jpg

front view as in 1 above.
Top view as in 2.

Then if you move the knee back you can reposition the boring bar and do the bore at the same time, same setting.

Then with a cranked tool you can face off both ends of the cylinder by raising and lowering the knee and moving it in and out.

So you get the radius, the bore and both ends all done from the squared off valve face. As view 3.

If you get scrounge a large enough bearing say 2" you can cut an R8 direct on one end and have a nice stiff boring bar.

I can't help with any bearings unless you can get away with 25mm or 1" as that's all i have on the shelf.

.

Davek0974
01-30-2009, 04:12 PM
Thats an interesting setup John, i probably would not have got there if i sat and stared at it for weeks!

I can understand the idea of line boring the cylinder and saddle at the same time as only the X axis will be moving and the sliding pillow block can acommodate the movement.

However, when you say cut the faces of the bore with a cranked tool and shift the knee etc, won't the pillow block bend the boring bar or am i missing something??

Thanks go to Ian too for the PM, another variation on the job.

Dave

John Stevenson
01-30-2009, 04:22 PM
However, when you say cut the faces of the bore with a cranked tool and shift the knee etc, won't the pillow block bend the boring bar or am i missing something??

Dave

Did I forget to mention the rubber boring bar :rolleyes:

OK forget all the last bit except you can do the end closest to the spindle with a short bat, then spin the casting round, clock up so the bore and radius id parallel to the bed then face that end.

Also possible to drill the end cover holes at the same settings while the head is horizontal.

Just many ways to de the same job.
i had originally though about doing this on a Horizontal used as a boring mill, that's where I got the bit mixed up when i transposed from Horizontal mill to vertical with the head slewed over, [ my story and I'm sticking to it. ;) ]

.

Davek0974
01-30-2009, 04:48 PM
Ahh, i see now, yes a horizontal / vertical exchange could cause some confusion:)

So i have a few viable options, forgetting the mega flycutter as a step too far.

One...
Using the rotary table fitted with an extension table and a suitable cutter to do the saddle with the bore done using a boring head.

Two...
Johns neat line boring idea for bore and saddle.

Three...
Something else? I am beginning to be able to see pro's and con's now which is good as it means i'm examining the job more thoroughly. I'll get out in the shop at the weekend and do some mockups.

Thanks all for your efforts so far.

Dave

lane
01-30-2009, 07:57 PM
As usual John solved the problem again.