Help! Needing a large diameter accurate hole

[Noods]

I think if you need accuracy and a pressed fit you need to do it the hard way and drill it inaccurately but slightly undersized. You then take the time to finish it accurately by hand. You’d be surprised what you can take off to a nice tolerance with a good round file and some basic abrasives. For 12mm thick I think you can realistically exclude hole saws and cone cutters. They are not really suited for that gage. If you need a 26 use a one inch black smiths drill, clamp it down well and just go steady away, nice and slowly with a good cutting compound. Then take her to her tight tolerance by hand.

Remember I do av a big one Rich! Pillar drill that is 7ft high..

 

[Noods]

If it doesn't work you could set it up like a line borer to cope with any side loading.

What is a line borer mte ?

 

[Burdekin]

What is a line borer mte ?

They're used for boring out holes, the one we had we just made and had a bearing assembly either side of the item being bored with a shaft going through and a cutter fitted in the shaft. We used air to drive the shaft.

So for yours to make it more steady you could weld a simple bearing arrangement above to stop lateral movement. But that would most likely mean extending the shaft of the fly cutter if it wasn't long enough so getting a bit over the top for the one hole.

Attached a pic showing the type of thing we use to use.

 

[Richard.]

This is an instance where size doesn't really matter.

If the chuck is on a taper without a drawbar (JT, MT or both) then putting any off centre loading on it can release the taper.

You might get away with it 50 times, you might not do it once...

And I think that’s the least of his worry’s. Consistently feeding that bar though at the rate it wants to cut is going to be a challenge without some form of more sensitive feed than the typical pillar drill offers.
I’m sure Noods will let us know if it was successful or not.

 

[Noods]

And I think that’s the least of his worry’s. Consistently feeding that bar though at the rate it wants to cut is going to be a challenge without some form of more sensitive feed than the typical pillar drill offers.
I’m sure Noods will let us know if it was successful or not.

I’m working on it already mte feed wise and lateral wise... my pencils on fire..... x will let you know obviously..

 

[fizzy]

Just ask these blokes - sorry couldn't resist!

 

[brightspark]

I’ve ordered these from an engineering company.. worth a try hey....

https://www.ebay.co.uk/itm/302166919392

X

bearings in the drill aren't designed for fly cutting with a sideways load it will chatter like mad

 

[Onoff]

I've done 70mm in 6mm thick st/st plate with an ordinary Starrett in a pillar drill (Rexon).

 

[brightspark]

I've done 70mm in 6mm thick st/st plate with an ordinary Starrett in a pillar drill (Rexon).

it wont have done the drill or the motor any favours

 

[knighty]

I did 2 x 120mm holes through 12mm ali with a battery drill

ali will be miles easier is you can switch to that instead

 

[Onoff]

it wont have done the drill or the motor any favours

The drill survived but the Starrett bit the dust. Can't remember if I got one hole or two out of it...had to use plenty of spray cutting fluid. Some pink stuff I got off the pipe fitters.

 

[Barlidge]

I believe the problem with the Starrett style cutter in deep material is relieving the swarf and controlling the speed, I have a 96mm hole to do in 20mm steel plate at some point.

 

[8ob]

I believe the problem with the Starrett style cutter in deep material is relieving the swarf and controlling the speed, I have a 96mm hole to do in 20mm steel plate at some point.

Spot on Bruce, nice and slow, decent amount of pressure,lube and keep the cut clear with a blow gun as you go, have done some very thick plate like this. That said I would not rely on a starret to give a press fit for a bearing, probably best to get within a mm with a hole saw a ream to size.

Bob

 

[eLuSiVeMiTe]

I believe the problem with the Starrett style cutter in deep material is relieving the swarf and controlling the speed, I have a 96mm hole to do in 20mm steel plate at some point.

Slightly off topic. Using bosch hole saws on thick timber/mdf/chipboard
Il start the hole off. Then drill holes around the diameter to allow the teeth to clear. May help relive the swarf.

 

[Pete.]

I once had to get up on an ally tower and push a 150mm diameter starrett cutter through a 32mm thick web of a huge RSJ with a gut buster drill. Got 3 or 4 done in a 8hr shift though I couldn't even do it nowadays.

Done loads on a pillar drill all different sizes. Slow speed and heavy on the handle but keep pecking often and use a good oil.

 

[eLuSiVeMiTe]

I once had to get up on an ally tower and push a 150mm diameter starrett cutter through a 32mm thick web of a huge RSJ with a gut buster drill. Got 3 or 4 done in a 8hr shift though I couldn't even do it nowadays.

Done loads on a pillar drill all different sizes. Slow speed and heavy on the handle but keep pecking often and use a good oil.

reminds me of another long day drilling 12 holes 60mm through rsj sandwiched between 4 2x9 tantalised sds with a clutch thankfully.

 

[brightspark]

I believe the problem with the Starrett style cutter in deep material is relieving the swarf and controlling the speed, I have a 96mm hole to do in 20mm steel plate at some point.

no problem, doing it on a faceplate in the lathe at slow speed with cutting compound . I use a wooden piece of plywood between the job and faceplate

 

[bigegg]

Can you not cut a bigger hole and use a pillow block?

 

[RichardM]

Can you not cut a bigger hole and use a pillow block?

Seconded:

https://www.ebay.co.uk/itm/8-10-12-...hash=item3d39323a5b:m:mYVpVpd5FWksXafGx67vG6Q