How to: milling machine ways attachment

drcoelho · Feb 2, 2019

I'm quite green, so please be kind. I'm planning on building an attachment to go onto the horizontal ways of a Deckel FP1 milling machine. The ways has two parallel dovetails. The attachment will be ductile iron sand cast and I'll be creating the dovetail in two steps:
- machine the dovetail
- manually get it super flat
There are two parallel dovetails, each roughly 12" in length, dovetails are 0.5" inset at 90 degrees.

I have only a milling machine (Deckel FP1, very accurate), no surface grinder. I have no experience doing the above and no experience scraping, etc.

My question: is it realistic to mill the dovetail, and then move directly to hand honing to get a flat surface (or is this even necessary?), and then finally moving to scraping? e.g. can I get the dovetails sufficiently flat on the mill to not need a surface grinder?

Demon69 · Feb 2, 2019

drcoelho said:
I'm quite green, so please be kind. I'm planning on building an attachment to go onto the horizontal ways of a Deckel FP1 milling machine. The ways has two parallel dovetails. The attachment will be ductile iron sand cast and I'll be creating the dovetail in two steps:
- machine the dovetail
- manually get it super flat
There are two parallel dovetails, each roughly 12" in length, dovetails are 0.5" inset at 90 degrees.

I have only a milling machine (Deckel FP1, very accurate), no surface grinder. I have no experience doing the above and no experience scraping, etc.

My question: is it realistic to mill the dovetail, and then move directly to hand honing to get a flat surface (or is this even necessary?), and then finally moving to scraping? e.g. can I get the dovetails sufficiently flat on the mill to not need a surface grinder?

Just mill your features and go straight to scraping. Be nice to see some pics of your project if possible

Cole2534 · Feb 2, 2019

Do you have a surface plate? If so, mill it then blue it up and see how it prints.

DMF_TomB · Feb 2, 2019

depends on mill and experience of operator. holding a .0003" per 40" tolerance is quite common on a cnc mill. got to watch part warping from its own weight and warping when unclamped. if not careful you can have trouble holding a .002 per 40" tolerance. for example part machined flat .0001" per 40" and when unclamped its bowed .010"

drcoelho · Feb 2, 2019

Cole2534 said:
Do you have a surface plate? If so, mill it then blue it up and see how it prints.

Yes, I do have a surface plate.

drcoelho · Feb 2, 2019

DMF_TomB said:
depends on mill and experience of operator. holding a .0003" per 40" tolerance is quite common on a cnc mill. got to watch part warping from its own weight and warping when unclamped. if not careful you can have trouble holding a .002 per 40" tolerance. for example part machined flat .0001" per 40" and when unclamped its bowed .010"

Manual mill (FPS 300 M/Deckel FP1), very accurate (brand new machine from germany). Operator: inexperienced but very detailed and patient

The part itself is cast ductile iron, structured as a box with ribs, so it'll be quite stiff.

DMF_TomB · Feb 2, 2019

drcoelho said:
Manual mill (FPS 300 M/Deckel FP1), very accurate (brand new machine from germany). Operator: inexperienced but very detailed and patient

The part itself is cast ductile iron, structured as a box with ribs, so it'll be quite stiff.

.
ductile cast iron occasionally has hard spots. harder spots will mill higher as mill wont bite in as much at those spots. hard to describe. some bad castings can easily have .0005" high spots in sync with noticeable color differences in the metal. different metal color cause metal is not all same like it wasnt mixed too well. usually its more that partially oxidized metal slag is mixed in at spots.
.
hard to describe but after machining a few thousand castings you learn to recognize hard spots. picture shows grain of rice size hard spots of slag. can easily dull mill

Demon69 · Feb 2, 2019

So the plan is to machine this widget on the Deckel, then remove the table/subtable and fit your widget in their place?

If so, mill the dovetails, remove the table, scrape the widget to the ways of the machine. What do you have in mind for a gib?

drcoelho · Feb 2, 2019

Demon73 said:
So the plan is to machine this widget on the Deckel, then remove the table/subtable and fit your widget in their place?
View attachment 248753
If so, mill the dovetails, remove the table, scrape the widget to the ways of the machine. What do you have in mind for a gib?

Not exactly, this is a widget (FP1 Riser) that sits on top of the horizontal ways in replace of the vertical milling head. So much easier, just remove the vertical milling head and match the widget to the horizontal ways. No need for gib, this thing just clamps onto the dovetail using a Deckel style eccentric clamp.

drcoelho · Feb 2, 2019

DMF_TomB said:
.
ductile cast iron occasionally has hard spots. harder spots will mill higher as mill wont bite in as much at those spots. hard to describe. some bad castings can easily have .0005" high spots in sync with noticeable color differences in the metal. different metal color cause metal is not all same like it wasnt mixed too well. usually its more that partially oxidized metal slag is mixed in at spots.
.
hard to describe but after machining a few thousand castings you learn to recognize hard spots. picture shows grain of rice size hard spots of slag. can easily dull mill

That is very interesting. The foundary I'm talking to offers varying qualities of Ductile Cast Iron, and I'm presuming if I go with the highest quality they offer, this would help?

drcoelho · Feb 2, 2019

Interestingly, I was looking at a photo of an FP1 Slotting Head, and Deckel didn't scrape it, looks like it was just milled flat. Thinking if I can mill the dovetails accurately enough, maybe scraping not required. The only purpose of the horizontal ways is to allow different heads to be slid on and locked in place, geometry is important, but it's not used dynamically during milling operation.

Demon69 · Feb 2, 2019

drcoelho said:
Not exactly, this is a widget (FP1 Riser) that sits on top of the horizontal ways in replace of the vertical milling head. So much easier, just remove the vertical milling head and match the widget to the horizontal ways. No need for gib, this thing just clamps onto the dovetail using a Deckel style eccentric clamp.

Hehe, that makes things a little easier then

You might be able the get away with just milling. You could relieve the centre a touch so the bearing surfaces are assured to come together at two points, not by much, just so as it clears. This could be done to all bearing surfaces.

Not sure how the clamp goes but the same principles could be used, looking at those 2 bolts id imagine they already are.

Can check your bearing with blue, scraping for final fit would be the next step if you thought it necessary, still taking out the centres of those surfaces.

Demon69 · Feb 2, 2019

Looking at these might make a bit more sense.

Full bearing

Centres relieved

For your riser you could blue it up, bolt it down and see what you have bearing wise. If youre good there and your alignments ok you could dodge the scraping.

drcoelho · Feb 2, 2019

Very interesting. Checkout this photo, this is what I'm actually trying to make. Note how Deckel reduced the contact surface to just both ends, similar in concept to what you are getting at.

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