[Newbie] MT3 vs R8

@mickri
You raise a good point about the reuse of tooling on the lathe.

I’m going to look at both the RF-40 and the Long Chang LC-30A today.
We shall see how they check out.


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mickri said:
Buy metric ER collets because there are no gaps in coverage. Imperial ER collets have gaps.
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FWIW,
stupoty said:
I Didn't know the imperial ER collets had gaps.
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FWIW, I have a set of Imperial ER32 collets in 1/32" steps and there are no gaps in coverage. The clamping range of each collet is more than 1/32". There are gaps in an ER32 Imperial set in 1/16" steps because the clamping range isn't that large. I don't know about other ER sizes.

Tom
 
mickri said:
Come on guys. Debating MT3 verses R8 is just splitting hairs for the sake of argument. For all practical purposes at the end of the day there isn't going to be any difference between the two.

When I was in your position just starting out and not having a couple of tons of money to spend I decided on ER collets because I could use them on my lathe and on my mill/drill. R8 can only be used on the mill. You will also need a collet system for the lathe. By the time you are done you will have spent twice the amount of $$$ or more and not gained anything over ER collets. I also think that ER collets are way simpler to use then R8. With R8 you have to loosen a drawbar and pound on it to free the collet. Then screw on the new R8 collet and tighten everything back up. I have to stand on a stool to deal with the drawbar. With an ER to R8 adapter or MT3 adapter for that matter once you have the adapter in your are done with the drawbar. I have never touched the drawbar after the adapter was installed. Changing tooling with ER collets is a breeze. Takes no time at all. Buy metric ER collets because there are no gaps in coverage. Imperial ER collets have gaps.

Davidr8 the RF40 will be a way better machine then the RF30. If it is in you budget buy it and get on to making chips.
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Chuck, not to be contrary but there is a difference between an MT3 and R8 spindle. As has been pointed out, MT3 tooling is much more available/cheaper in Europe; same thing for R8 here. Due to the amount of taper that is locked into the spindle, it takes more force to release an MT3 collet or shank; it takes just a tap to release an R8 due to the very small taper engaged. Here in the US, it is more common to see an R8 machine; not sure what the situation is in Canada.

The "gap" you mentioned has been raised before but since almost all the tooling we use in the US is Imperial, buying metric collets is not as wise a choice as it might seem. This is more for David's edification but an ER collet grabs most solidly and is most accurate when the collet fits the nominal size of the tool being used. While you can grab that tool with a metric collet it might be just a tad off compared to an Imperial collet. For example, for a 3/8" tool we would use a 3/8" Imperial collet but would probably use a 10mm collet in the metric system. That 10mm collet has to collapse almost 0.020" to grab that tool and that will impair accuracy to a small degree. Yes, it will grab the tool but not as well as a 3/8" Imperial collet will, and this applies across the range.

I agree that ER collets can be used on the lathe as well and this is where having a metric collet set might be more practical but for the mill I suspect an Imperial set is going to be more useful, at least in this country.
 
Long term I think the main advantage to R-8 is many of the larger hobby sized mills use it, so tooling can transfer if you eventually replace the mill. MT is also out there but doesn't seem as dominant. There are several competing tapers on vintage machines, the Brown and Sharpe tapers being a popular alternative on US machines which I think cuts into the uniformity of the MT.

I haven't gone looking for MT3, but MT is very common on lathes so I expect you can find most anything you would need.

The point about sharing with a lathe is also a thing. Very handy in some cases, but probably not a major factor. My Clausing mill is MT2 as is the tail stock of my 10x24 lathe. There are a couple of bits I can see sharing, but the vast majority of my MT2 tooling is probably more of a mental exercise as they are strongly associated with one machine or the other.

There are lots of adapters to fit both R-8 and MT. Many boring heads and drill chucks can be bought with a threaded hole allowing you to use the taper of your choice. I have threaded MT2 adapters which will work with my ER collet chucks, boring head and some of my drill chucks.


Unless it is a very unusual taper I don't think I would get too hung up on it. R-8 probably has a modest advantage in price and availability, but MT3 is not rare.
 
On a Rung fu mill, the MT3 could give a slight advantage due to its shorter length, might save having to move the head to swap collets.
 
Superburban said:
On a Rung fu mill, the MT3 could give a slight advantage due to its shorter length, might save having to move the head to swap collets.
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Well I'll be dipped, you're right. I only have one MT3 for my lathe and I'd never compared it to the R8. MT3 was 1/2" shorter. Guess it's no big deal on the square column Rf40 but that could on the 30/31.
 
The threaded MT3 collets are about1/2" to 3/4" shorter then the tang style MT3's.
 
Mine was the threaded type for the headstock of my 9x20.
 
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