Newbie question: how do I machine this? (Drawing attached)

[Aegeon]

I need to make a router mouting plate for a cnc router table I'm putting together. I'm new to machining, but have an Enco benchtop mill (RF-30 clone). I can handle the straight cuts, drilling the small holes, etc, but my question is about the large (3" diam") hole I need in the center of the part... How could I go about getting this done w/ my mill? I'm not opposed to buying tooling (I'm slowly stocking up, although I know I can't afford a rotary table), I just dont know what I'd need...

Any help appreciated.

Aegeon

[Chris D]

Drill a starter hole with the largest drill you have then,

using an adjustable boring head, take a series of cuts until you open up the hole to the size needed - boring heads can be purchased from Enco farily reasonable in price. I bought one of the really cheap ones and it has been working fine.

You could make a fly cutter ( a round tool holder that can hold a 1/4" tool bit (the kind used on manual lathes - usually HSS). Then bore a hole, move out the tool bit a little, bore again, just like with the boring bar, but less accurate to some degree.

A hole saw may also work, but I don't think using a 3" hole saw will give you a 3" hole accurate enough - you would still need to finish bore it - so use an undersize hole saw to create your rough hole.

Hope this helps a bit!
Chris

Originally Posted by Aegeon I need to make a router mouting plate for a cnc router table I'm putting together. I'm new to machining, but have an Enco benchtop mill (RF-30 clone). I can handle the straight cuts, drilling the small holes, etc, but my question is about the large (3" diam") hole I need in the center of the part... How could I go about getting this done w/ my mill? I'm not opposed to buying tooling (I'm slowly stocking up, although I know I can't afford a rotary table), I just dont know what I'd need... Any help appreciated. Aegeon

[DareBee]

You should get a boring head set.
http://www.mcmaster.com/ctlg/DisplCt...&CtlgEdition=&
You can get a set like that for a couple hundred at KBC tools

[Aegeon]

Thanks for the advice...

Looking at the Enco site, most of the boring heads are 2"-3" diameter... Does this mean I would need a starter hole at least this size before I can use the boring head? I'm unfamiliar with these tools, but it appears that the boring bars slide through the head, so the minimum possible diameter would be close to the diameter of the head itself (Please let me know if I'm wrong here). The largest drills I have are 3/4", so I'm not sure how I'd get the starter hole... Any suggestions?

Thanks again...

[anoel]

YOu could always do a Request for Quote here. I'm sure that one of the members here would be more than happy to make one or a set for you for a fee...

[DieGuy]

Originally Posted by Aegeon Thanks for the advice... Looking at the Enco site, most of the boring heads are 2"-3" diameter... Does this mean I would need a starter hole at least this size before I can use the boring head? I'm unfamiliar with these tools, but it appears that the boring bars slide through the head, so the minimum possible diameter would be close to the diameter of the head itself (Please let me know if I'm wrong here). The largest drills I have are 3/4", so I'm not sure how I'd get the starter hole... Any suggestions? Thanks again...

Generally not. Most boring heads are rated at the max size and will center the shank of the boring tool on the center of the spindle. So a starter hole of 3/4 in should be plenty and subsequent cuts with the boring head should be controlled amounts like 0.050 a pass till you get close. then smaller and smaller cuts to get to the finshed size.

[ViperTX]

If you start at 3/4 inch.....it will take you forever to bore the hole.....use a hole saw, or a fly cutter.....you could adapt a carbide cutter to the 3" boring head to do the initial hole at 2 3/4 inches.....if you have a rotary table you could use a mill and rotate the table slowly to get close to 2 3/4 and then switch to a boring head....buy a 3" boring head with the carbide cutters.

[DieGuy]

As the man said he has limited tooling, One alternative is to make a boring head to fit you mill. All you really need is simple slot to hold the tool with set screws,a fly cutter can double for this boring bar. Scribe the hole out and rough it out freehand with the mill, leaving about 1/8 inch all around to remove (draw 2 sets of lines if needed, the rougher @ 2 3/4 and the finisher @3). Then set the tool in the boring bar to clean up the hole. and measure from the tip of the tool to the back of the boring bar and measure the cleaned up hole.

Loosen the set screws and reposition the tool into the work piece some amount by measuring off the back of the boring bar and cut again, Sneak up on the finish diameter, remember the distance you move the tool is on the radius of the hole. A pair of calipers is adequate for this kind of work. you really only need to get within a few thou for a clamp. When you make the clamp cut it will probably spring open some anyway.

[Jokerr]

i have not seen the center where the bore is placed. then i have not seen the hight or from wich end the center hole will be for the 1.5 diameter

[DareBee]

Originally Posted by Aegeon Thanks for the advice... Looking at the Enco site, most of the boring heads are 2"-3" diameter... Does this mean I would need a starter hole at least this size before I can use the boring head? I'm unfamiliar with these tools, but it appears that the boring bars slide through the head, so the minimum possible diameter would be close to the diameter of the head itself (Please let me know if I'm wrong here). The largest drills I have are 3/4", so I'm not sure how I'd get the starter hole... Any suggestions? Thanks again...

The boring bars can be mounted as you are thinking, but there are holes that put the boring bar straight out the bottom as well. If you look at each individual boring bar they will list a minimum bore size, you could bore an 0.080" hole with a 3" boring head and the right bar.
As far as doing the starter hole, once you have scribed the hole drill it 3/4 then drop an endmill in there and drive it around by hand to remove the excess stock. This is an eyeball operation to stay inside your scribed line. Then you will not have much stock left to bore.
Realistically though it will take no time at all to bore that part from 3/4 to 3", it is very thin and you can take 0.050 cuts easily.

[Aegeon]

Thanks, everyone, for your replies. I'm now looking into getting a boring head & bar set from Enco. They'll have to be the relatively cheap brands (some of those high-quality sets are $400+), but the parts I'm making really dont have to be that accurate.

I know there are plenty of experienced people here that could knock these (I need 2 made) out in 20 minutes, but every little piece I spend hours fabricating myself adds a bit of experience (not to mention another excuse to buy new tools).

I appreciate all the feedback. I'll let you know how things turn out.

Aegeon

[take a cut]

a hole saw that large in alum will want to bind if you go this rout e use lots of coolant and a wire brush to clean the chips from the teeth as you peck up and down in the part. 2 3/4 dia should be good. then any of the above mentioned boring setups will work fine to finish. if you go with a tool and a bar sticking out take a test bore then set up a dial indicator to touch off at the tip of the tool in the mill rotate and adjust using the dial to get size. this should work