Using a milling machine to make big holes?

[TheJoker]

Hi guys,

I've got a small Axminster SIEG Super X1 Micro-Mill and sometimes I want to make big holes. Say more than 20mm up to, say 50mm. Mainly stuff like, for example, a clamp that would go on a motorbike front fork, maybe a handlebar. The depth of the hole would be no more than 25mm as that's kind of the thickest billet I can think of working with.

As I don't have a lathe, I'm wondering if there's some way to cut these sort of holes using the milling machine. There's no urgency, so I don't really care how quickly it can be done. I do have a small rotary table but winding that around for such a big hole is a bit tedious.

Anyone got any cool tips? Is there a tool out there that I could use?

 

[gavuk]

Hi we used to use an adjustable boring head boring head.......or......boring head and tools....drill or holesaw as large as you can then use this type of head to produce final size and depth...........G

 

[Shox Dr]

Yup Gav hit the nail on the head.

Rdg Tools do some nice boring heads. (Well they must be; I bought one)

 

[Shox Dr]

Here you go the first one on the page is the one I bought, very well made, esp for the price. And it's in MT2 so will fit your mill

http://www.rdgtools.co.uk/acatalog/BORING_HEADS__2_MORSE_TAPER.html

 

[snowcat]

the indexables are an outstanding price, might try a small head myself and see how it stands up.....

 

[TheJoker]

Thanks gents! I was under the impression that a boring head was only used to skim holes, such as cylinder bores?

So, let me see if I got this right.

The top bit, boring head I assume, goes into the chuck of the milling machine. Then the middle bit goes into the hole of the top bit? Then the cutting bit, at the bottom, goes into the hole of the middle bit? Middle bit can be adjusted to different hole sizes?

Is that right or where did I go wrong?

Thanks again!

 

[gavuk]

i would suggest getting someone to run you through setting up ,speeds and feeds and practise on alluminium,great bit of kit ,not sure how well a micro mill will cope,used to use on a bridgeport to machine bearing fit holes in plate,what type of mill are you using Shox?

 

[Shox Dr]

Tom Senior Light Vertical, and a Bridgeport


Joker in the case of the one I linked to, you would take out your chuck and replace it with the boring head

 

[Shox Dr]

the indexables are an outstanding price, might try a small head myself and see how it stands up.....

The one I linked to is as I said very nice, I wasn't bother about the other bits that came with it. I cut Dural and CRS with it and so long as you get the cut/feed rate ball park it does a good job

 

[gavuk]

Can a micro mill handle the out of balance of a boring bar? ,never had experience with them ,i know its not the same as huge cutter and cuts can be very light etc,still a big ask of a little mill?

 

[Shox Dr]

A mate of mine has a similar machine to Jokers. He uses a boring head on it, he does say it's hard slow work.

 

[TheJoker]

Good tips here guys! Much appreciated!

One question though. Does the boring head make one groove (i.e cut) in the metal, or does it "drill out" all of the material? Think hole saw vs drill bit?

Oh, and Aluminium is pretty much all I do on the machine.

 

[Shox Dr]

Boring heads really should only be used for final cutting in that you have ruffed out the hole size first by whatever means. Have a look in the links section of the site, you will see a link at a very good set of videos on milling

 

[TheJoker]

Thanks! Will look at the tutorials now.

So there's no real way of cutting a hole, in one go?

 

[MG David]

Does the cutter sit outside the diameter of the head meaning that you can only bore holes greater than the head's diameter?

I may need to bore a hole to take an exhaust seat that is about 30mm in diameter. If the cutter sits outside the diameter of the head those all seem to big.

 

[wyn]

You could use mag drill broaching cutters with an MT2 adaptor to fit the milling machine.

But they might only have a tang and no thread for a drawbar.

This sort of thing

 

[stormin]

Does the cutter sit outside the diameter of the head meaning that you can only bore holes greater than the head's diameter?

I may need to bore a hole to take an exhaust seat that is about 30mm in diameter. If the cutter sits outside the diameter of the head those all seem to big.

Most boring heads I've seen have holes for horizontal and vertical setting of the boring bar so they can be used for small and large holes. The disadvantage of setting the bar vertical or inline with the spindle is that you an only bore to the depth of the bar and you will get more spring in the tool reducing accuracy.

 

[TheJoker]

You could use mag drill broaching cutters with an MT2 adaptor to fit the milling machine.

But they might only have a tang and no thread for a drawbar.

This sort of thing

Wyn, could you please explain a bit more for a newbie/daftie like myself? I don't really get it.

 

[snowcat]

biggest problems I have found is due to either feed rates, these need to be slow and steady, and chatter especially when clamping irregular parts....

You can take large cuts, but not with a long tool, I often grind a piece off tool steal to sit directly on the edge of the head much like the indexable ones I can normally cut the tool width when rouging around 1/4" a time, takes some balls the first cut mind to make sure the clamps have the work properly... feed has to be aggressive over wise the tool overheats and loses the edge..

I personally think there one of the harder tooling's to get to work properly....

 

[shenion]

What about doing it the other way around: Rotate the work using a rotary table. Then could do any size hole with just an end mill.