[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

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]

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]

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

[take a cut]

with 2 parts you should do this setup clamped together as you dont want to hit this size twice.

[DareBee]

I find that hole sawing anything more than 1/4" thick (especially aluminum) works best with "chip hole".
I mark the part with the hole saw then drill a 1/4" (or something) in the ring that the hole saw will cut. This helps break the chips down as well as gives them somewhere to fallout. Use lots of coolant as well.

[Kookaburra]

As the guy's said a boring head is the best way to finish the hole. To achieve a starter hole big enough to start boring, you could do one of the following. If you have a rotary table that can be mounted on its back, you could use an end mill set to a distance away from the center of the line and simply plunge the cutter and rotate the job (you could finish the bore this way as well but a boring head will achieve the best result). Or, if you have not got a rotary table (or a big enough hole saw), you could use an end mill to mill through a square making sure that across the corners of the square you are milling is smaller than the finished diameter of the hole, then fininsh the hole with a boring head. Keep in mind that this option will mean that you will be taking intermittent cuts a first and you should adjust your radial cut depth to suit.

[Phooey]

Hi, Im a newb too... but why all this talk about hole cutters and boring heads, couldn't you just take a 1" flat endmill around that hole? you could get it in two depth cuts and if tollerances are critical just set your tool wear corrrectly and do two or three finish passes at .01. when ive been concerned about throwing the inside peice i've just broken the arc, set to single step, clamped it when it stopped after half of the final depth cut (with the spindle OFF), and unclamped and removed it after the second half of the cut (then take single block off and go through the rest of the opperation). any jitter that occurs during this doesn't matter because it's only a couple 1/1000s and the three finish passes clear allot more material than that out anyway.

[dfranks]

I'm new so correct me if I'm wrong. Since it's just cutting out the a 3" circle and it's only .375 thick couldn't you cut out a wood template, getting it a perfect as possible. Clamp it to your stock and then using a router with a small straight bit with a roller bearing guide cut the circle out in multiple passes?

[cncsdr]

why not just circular interpulate it in a mill?indicate it in and let it rip

[whateg01]

why not just circular interpulate it in a mill?indicate it in and let it rip

I could be wrong (it's happened before), but I gather from the posts that the mill is manual. The CNC device is where the parts will go when they are finished.

I once read that there is more than one way to skin a cat. The main thing is that in the end, the cat is skinless.

Dave

[rcazwillis]

Depending on the mill, check out www.littlemachineshop.com. Good prices on chinese made tools. I purchased one and have been very pleased. First time I used it, I went from 3/4" to 2 1/2". Spindle clamp turned out nice.