Trouble with a part

[sconisbee]

This week brings me a new challenge, now i have a few ideas how to do it already, i figured i would consult the masses as it were. Theres a *ton* of collective knowledge on here so here goes.

I have this part to be made out of acetal or similar (no form tools please! ) its a one off, and I have a couple of ideas on how to do it without CNC but before i put cutter to plastic i figured i would ask if anyone else has any ideas.

Thanks in advance.

[Your Old Dog]

Do you have a mill?

Is the stock already trimmed to size (do you have room to grip the stock)?

[DickDastardly40]

Scon,

Perhaps you could fix it to a 90 deg angle plate and flycut it with a flycutter/boring head set to the required radius or

In a similar way to this (not my work)



with a sanding drum made to the correct radius (not sure how or if acetal sands).

Regards

Al

[Doc Nickel]

Actually, a form tool might not be a bad idea, but I think you'd spend more time making the blade and some sort of arbor for it, than you would doing the job. Clamping's going to be iffy no matter what method you use, due to the thin cross section. Chances are you're gonna have to leave it long in some dimension, and mill to size as a final step.

Other options- meaning how I might try 'em, not necessarily that they might work.

A lathe faceplate with an angle block, and "bore" the radius. Gonna be slow unless you can properly counterweight. Maybe a slow backgear speed, but with a mill/cutter in something like a toolpost grinder, make the net shape in a single pass?

Angle block in the mill, with a boring bar, fly cutter of the proper diameter, or circular cutter (like from a horizontal mill.)

Extra-long endmill, and an angle block on a rotary table. (A 7" endmill might get kind of spendy, though. )

Tilting the mill head can get you an approximate radius, but as I recall, it's not a true circle.

Let us know what you try.

Doc.

[John Stevenson]

First we need to know what machinery is available
No good saying tilt the head on the mill if it won't

.

[sconisbee]

Other options- meaning how I might try 'em, not necessarily that they might work.

A lathe faceplate with an angle block, and "bore" the radius. Gonna be slow unless you can properly counterweight. Maybe a slow backgear speed, but with a mill/cutter in something like a toolpost grinder, make the net shape in a single pass?

Angle block in the mill, with a boring bar, fly cutter of the proper diameter, or circular cutter (like from a horizontal mill.)

Extra-long endmill, and an angle block on a rotary table. (A 7" endmill might get kind of spendy, though. )

Tilting the mill head can get you an approximate radius, but as I recall, it's not a true circle.

Let us know what you try.

Doc.

I figured i would have to leave it long anyway so thats less of an issue, thought about the lathe, the only thing stopping me from doing that is counter balencing it properly currently,

Running a 150mm diameter flycutter would work and the mill could handle it (Gate Profitmill with INT 40 spindle 3hp) but i have to admit that idea kinda makes me nervous a little lol!

Tolerances are way open well non existant really as only the holes need to be +/- 0.5mm positional wise. The mating part is an extruded almuminum boom so thats likely not going to be a perfect radius anyway cause the boom isnt round. Only got the drawing through thismorning and im still mulling on it while waiting for material.

one thing i did think of though it would be really really slow on a manual machine, i did figure that if it came to it i could surface the arc by kellering with a large ballnose cutter.

I have a really somewhat simple but kinda awkward in its own right idea that im keeping secret till i can figure out if it will work lol, if it does ill post the results and the method on here.

[sconisbee]

First we need to know what machinery is available
No good saying tilt the head on the mill if it won't

.

DOH!. i did mean to mention that part

Machinery available is:
a 3hp Gate Profitmill, bridgeport clone but with INT40 spindle
12x36 gearhead lathe, and a 18x72 belt drive lathe
and pillar drills, grinders, and other miscellanious other paraphernalia to injure myself with!

[John Stevenson]

I have to do the same part from time to time also in Delrin.
These are terminal boxes to fit big DC fork truck motors after they have caught fire !

Mine are usually only 100mm square though.

I do these by standing vertical in the vise and using a biggish 3" boring head with side mounted tool use the quill to traverse down and the X axis to feed a bit at a time.

Because yours is 160mm long and you probably won't have that travel on the Gate quill ? you can always swing the head thru 90, use a boring head or fly cutter [ they are not that scary if you don't get in the way ] and with the work laid flat in the vise traverse the X for travel and the knee for feed.

.

[J. R. Williams]

Plastic Part

I vote for a Bandsaw.
JRW

[Hawkeye]

TableSaw

Can you cut it like they make cove moulding on a table saw. Set a fence at an angle to the blade and run the workpiece through at an angle.

check this out. http://www.binkyswoodworking.com/CoveMouldingTip.htm

[Carld]

I like Sir John's method. Flycutters are not that dangerous if done with care and it's easier to get the radius you want. You can mount the work to an angle plate and use the knee feed to cut the radius if you don't want to lay the head over. Use a backing plate to support the work if the angle plate is not tall enough.

[jkilroy]

Stand it up, use a boring head

Stand the part straight up, setup a boring head to the proper radius and cut the part, no big deal. Take as many passes as required by your ability to hold the work.

[rkepler]

Stand the part straight up, setup a boring head to the proper radius and cut the part, no big deal. Take as many passes as required by your ability to hold the work.

Since Mr. Kilroy didn't mention it I'll make mention of a real easy way to set a boring head to cut a radius. Setup the work so the radius cut will be vertical (with quill feed) but with some clearance at the bottom of the cut. Touch off the edge of the work for a 0 point and back the table away from the work by the radius amount. Set the boring head so the tool just touches the work and you have the radius set to a pretty good value.

You can also use a flycutter for the cutting, it's just more finicky to set the tool on the radius.

[andy_b]

i think it would be a good job for a shaper.


andy b.

[sconisbee]

Can you cut it like they make cove moulding on a table saw. Set a fence at an angle to the blade and run the workpiece through at an angle.

Now thats pretty smart, dont have a table saw though

Johns method will work a charm but hes right about lack of quill travel its only got 120mm of quill travel. so ill probably do the head tilt trick (im not really looking forward to cranking the knee that much )

In the words of a somewhat famous character... I have a cunning plan!...which would be neat if it works and real handy for repeat jobs that i might have in the future. till i try it and things go bang im not saying anything more about that idea wont have the material till friday at the earliest so got plenty of time to plan