Colt Maxicut Forstner bits - deep boring test

[rsser]

I was sceptical about the Colt Maxicut Forstner bits as posted in the original group buy thread. But having ordered a couple with the MT2 Rotastop adaptor and 150mm extension, Brett (FenceFurniture) told me to get off my backside and try them.

So to test one at a demanding task I used a dense and cranky grained lump of redgum mounted on the lathe and bored endgrain with a 35mm bit down to 220mm. 1000 RPM. Colt suggest a speed range from 750 to 3500 and normally I'd run that size bit at about 250 in hardwood. The speed range for the Rotastop and extension is 500 - 1400 RPM.

I started without the extension and got nice chips to maybe 50mm depth. Then added the extension and proceeded apace. The result soon turned to dust but with cleaning out repeatedly the cut continued fairly quickly to the final depth.

Upsides: even with the extension which is fairly spindly (10mm OD cp. 3/4" on my custom-made job) the bit tracked straight and continued boring without apparent drama. The Rotastop and extension couplings entail an eccentric shaft and so are self locking. My existing MT extension fixes the bit with a grub screw and when bits approaching 50mm are used, slippage happens.

Downsides:

1. This test produced a big wear bevel on the chipping edges. Sharpening was required.

2. To clear shavings or dust in this application you either retract the bit or blow them out or use a wooden chopstick 'scoop' with the piece spinning (yeah, sounds odd but it works and is my preferred method). The retraction option was tried before adding the extension and the jam lock of the coupling failed leaving the bit to rotate in the work piece. Perhaps with more vigorous winding back, opposite lock would kick in. Whatever; after that I used the chopstick and blowout methods.

3. Half the edge, at the trailing end, of the two teeth were blued. Hadn't checked this before starting but don't expect they were there. And looking with a 30 X mag. loupe on the unused bit, the chipping edges are on the ragged side and of course there's no bluing. I could've just been hamfisted given the ease of progress.

Final judgement waits on more use. Certainly this was a tough test.

(And when I talked with Brett about the performance he told me I'd ordered HC steel bits, not HSS as I'd assumed . Well, I dips me lid to Colt cos at that it was punching above its weight. This test would likely have had a better outcome with slower speed and feed rate).

Past experience is shallow and deep endgrain boring on the lathe with sawtooth HCS and HSS bits from wherever. And some testing of a C/tec TCT bit.

With silica-rich or dense timbers, I wouldn't go back to HCS bits. Easy enough to sharpen but need it often. Conventional HSS lasts better but can generate of lot of heat depending on other factors as well. TCT puts up a good fight but leaves a poor finish which is not a problem boring pepper grinders but is a drawback doing stuff like napkin rings.

One big variable is the lathe tailstock quality. Affects bit tracking and so heat generation. Minimal play is best obviously. With experience of four brands of lathe, the Vicmarc tops the list and was used here.

After sharpening the bit I tried a second test on English Elm, a timber within the expected scope of HCS. The bit kept cutting chips down to the end at 160 mm. Clearance of chips through the flutes was efficient. RPM of 500. The bit got very warm but not hot and developed wear bevels just visible to my reading-glass assisted eyes. The self-locking couplers seemed to have seated somewhat and held more firmly this time around; getting them apart took a bit of effort.

Sharpening

It was about half an hour's work with diamond paddles to get the bit back in condition after the first test, working the chipping edge tops and putting some effort into the flutes. Starting with a medium grit paddle and then fine and super-fine. The nice feature about the bit is that the top of the chipping edge is co-planar with the dropped section of the rim so good registration of the paddle is easy to get. The flute on the other hand obviously involves a lot of steel, and it's not all that easy to keep a paddle flat so I ended up settling for an adequate rather than a good result there.

I haven't touched up the 'wings' (the raised part of the rim). Leonard Lee's sharpening book shows a jig for doing this to maintain the bevel angle. I'll have a shot at doing the bevel with a bit in a Dremel, inking the bevel first.

The included bevel angle (chipper top to flute) is about 50 degrees.

Summary

The cutting and chip ejection are better than garden variety saw tooth bits. Sharpening is easier. The quality of the HC steel is impressive.

For deep boring I favour an MT mount over a Jacobs chuck as there's less play. The Rotastop MT2 and the extension work well.

Heat is the enemy of Forstner bits and they have to be kept sharp. Leonard Lee recommends keeping them free of resin and applying dry lubricant before use.

I've put in an order for several Colt MaxiCut plus HSS Forstners. A 35mm bit will be about double the price of the same size unit from Carba-tec and that's quite a premium so I'm only ordering the sizes that will get regular use.

The geometry of the HSS bits differs from the HCS jobs so sharpening the chipping edge may not be as easy. They also have a pilot drill instead of a brad centre and that will be a disadvantage where a relatively flat bore bottom is needed.

Many thanks to Brett.

[NeilS]

Thanks Ern for the review. That's the same (main) use I intend for my Maxicuts and Rotostop extensions. Never having used them, I hadn't anticipated that the Rotostops might let go and leave the bit beyond reach. That would be a real PTA when deep boring, which I was planning on doing.

Did you reverse the lathe when retracting the bits?
.

[Harry72]

Jeez Ern that review was a bit of a bore

good job bloke

[rsser]

No Neil. That may encourage unlocking of the coupling.

After the 2nd test though I'm more confident of the holding power of the system.

[rsser]

Boom tish Harry ;-}

[Jim Carroll]

Ern how would they have gone at the more sedate speed of say 250-300rpm which is where I would normally run any forstner bit.

The speeds colt recommended generally would generate more heat and burn the cut more than allow the cutter to work properly.

This is probably where you are getting your blueing from overheating more than abrasiveness of the timber. This in turn gives you the blunt edge so no more shavings but chips.

[Tim the Timber Turner]

I agree with Jim.

Much too fast for a bit of that size, regardless of what maxicut say.

I have used my maxicut bits in redgum to 150mm without any sign of burning.

They would be no value to me if I had to spend 1/2 hour sharpening one after drilling only one hole.

Cheers

Tim

[FenceFurniture]

Jim, in the light of Ern's findings, do you think a one letter change to the thread title is in order?

[rsser]

Jim and Tim, yes, you're quite right and pondering this I decided to double check the lathe setup.

The speeds posted in the test report should be divided by about 3.

I was taking the EVS RPM read-out but the belt was on the high torque setting

Neil, to be clearer, after the 2nd test the components had to be separated by a decent tug on the spanners on the shaft flats.

And I should say that the lump of redgum I used in the first test was an A-grade pox. Dulls turning tools toot sweet and makes a Veritas A2 plane blade look like cheese. I'd chosen it thinking the bit was HSS, so all up, it was unwittingly testing to destruction.

And yes, can a mod change the post title to Colt? Was nowhere near cold

[FenceFurniture]

JThe speeds posted in the test report should be divided by about 3.

Ern, does that mean that the Elm test was around 160-180 rpm? Or had you changed the belt setting, and it was 500?

Cheers, Brett

[rsser]

No Brett, divide all those RPM numbers by 3.

[FenceFurniture]

I'm going to talk to Colt about a couple of ideas that I have, and also to find out how short the retracted pilot drill can be in the HSS MaxiCut plus Forstners (to get the minimum impact with blind holes). I imagine that if it can be retracted so that only 5-8mm is showing then it would be ok for most blind holes.

The other query I have (for here, not there) is what would happen if you started the hole with the pilot drill showing perhaps 20mm or whatever, and then remove it altogether when the hole was established a certain distance in? Would the forstner still track straight? I would have thought it would be pretty reasonable, given that there is the cylindrical wall of the forstner, and the rigidity of the RotaStop setup.

Another idea that I have for Colt is an HSS M2 Auger 3/4" by 230mm long, specifically for bench top dog'oles. Exit wounds would still be a concern (if unsupported). This has all sprung out of Groggy's Famous Hole Drilling Marathon. Groggy suggests that a Scotch pattern flute is best, but Colt use a Lewis pattern flute, so I'm not sure if they can do a Scotch. They did the British for a while there though.

Following on from that I want to see if I can get a 3/4" 5* FCE Brad Point made by them. I believe that the chip ejection going through a 100mm bench top should be ok, and it would definitely give a better exit wound. In fact, I've found that with a 10mm 5* I can get a very clean exit even using a hand held drill on an unsupported back. The trick is to know when you are about to exit and keep the revs up but with LIGHT pressure. Certainly the entry from a 5* is excellent - the hole edge is as sharp as.

[rsser]

Yeah, it'd be good to know why the diffs btwn the HCS bit and the HSS bit. They're substantial as far as I can see from the poor pics around.

And for a blind hole in the only application I have where that's critical, even the added depth of a brad point is unwelcome.

In terms of your 'other query', what happens with the HCS bit is that first the brad point engages, then the wings (or teeth if you like) engage, and then the chipping edges.

The wings are rather different from conventional saw tooth bits but are clearly critical in the bit tracking and may account for much of the quality I found (and cos there's less mass in them, for the bluing as well). So speculating, I can't see that a pilot hole would add much and may detract from performance if the brad point wasn't properly engaged from the start.

For turners, at a guess, a 1" auger would be of more interest being the long hole diameter for Crushgrind pepper grinders and maybe other mechanisms. Brendan Stemp prefers an auger over a saw-tooth or Forstner bit for this purpose and he makes a living out of this kind of work.

[FenceFurniture]

For turners, at a guess, a 1" auger would be of more interest being the long hole diameter for Crushgrind pepper grinders and maybe other mechanisms.

In for a penny, in for a pound. Augers come 230, 320, 460, 600mm lengths.
Pick a size.....I'm thinking 320

[FenceFurniture]

A few pics and diagrams that will be slightly better in resolution, but not great.

MaxiCut Depth Stop



Maxicut Forstner





MaxiCut plus Forstner





VHW Carbide plate Hinge Bit







or go to the website and look at pages...forget it...they're no better.