Do you use R8 collets? If so one easy fix is an ER collet chuck on an R8 fitting which will save  a lot of winding the head up and down.

On 10 September 2024 at 08:36 John Haine Said:

If so one easy fix is an ER collet chuck on an R8 fitting…

Please could you flesh out that idea with specific reference to the original post.

The justification you have given involves raising or lowering the head, which is not a factor I can see mentioned in or relevant to the original question. Even with cutters of different lengths, it is difficult to see how a particular collet system can compensate for this.

Please write down the steps necessary to change a cutter in an R8 collet (let us assume the cutter is on a 1/2″ shank and is being replaced by another one on the same size shank), including any movement of the machine’s head. Write down the steps to do the same for the same two cutters in an ER chuck and explain where one has a speed advantage over the other.

Now do the same for cutters of different shank sizes (i.e. where both collet and cutter have to be changed). Consider the case where the replacement cutter is already loaded into the appropriate R8 collet.

Right now, having thought about it for two minutes, I can see one advantage of an ER system in terms of speed: going from a 1/2″ shank cutter to a 12mm shank cutter (i.e. shank size changes but collet can accommodate both). As you have pondered on the matter in far greater depth than this before making you post, it would be most helpful if you could share those profound thoughts.

” I find changing between tools time consuming ” Surely it takes time to wind the head up and down so it must be a factor in the OP’s question

Well I don’t know about John but when changing between shank sizes and there for collets when using ER I don’t have to wind the head up and then back down much ( or sideways). Just need enough room to wind the nut down and a bit of clearance as the cutter can be pushed up into the collet for extra clearance say 20-25mm. If I were having to swap an R8 collet then it would mean and extra 50mm or so up and an extra 50mm back down.

Actual undoing and doing up is probably much the same be it R8 or ER so for me when changing between size shank the ER is faster than R8. Same shank size probably not much difference in time

MT is probably a bit less winding than R8 as you can tilt an MT piece of tooling so don’t need as much clearance height as R8 which needs to go in and out vertical and you also need to locate slot with pin.

Going over to TTS and making a lever action Drawbar would also speed things up but a bit spendy.

The ones I have seen of being used by members here were on Bridgeports that have a spindle lock but as you say may not be needed. This is the type of thing and it looks like he does not have a lock on his benchtop machine.

I simplified things on my mill by making some ER25 collet chucks with a 20mm shank and using a 20mm R8 collet in the spindle, like the Tormach ones that use 3/4 shank.  This means most of the time when using different cutters I can use the quill and not have to move the head slide.  I have to make some drill chuck to use the same system as I don’t have a full set of collets, but you could use collets for all tools. The length of shank is only about 50mm as that is all that is usable in the 20mm collet.  You still have to loosen the drawbar but it is far less than a full remove of the R8.

A butterfly impact wrench operated power draw bar system as per aftermarket units for Bridgeports should work fine given a suitable mounting. Several home shop designs can be found. The commercial ones also seem to use the same sort of impact wrench as a driver but with rather more sorted controls and air handling than the home shop versions. For which you pay £££ more. But they are, allegedly, plug and play.

Being an example of the largest square column bench mill design the Super Major is, in a practical (ie swarf limited) home shop context pretty much the equal of a Bridgeport in metal munching ability. So you might as well treat it as the same albeit re-packaged into a smaller format with the associated gains and losses.

Putting a conventional power drawbar set up will add weight to the head. It’s is already way too heavy for easy hand cranking up and down so not advisable unless you have power drive version.

Realistically the essential drawbar operated change is between cutter holder and drill chuck. No way round that or the head lifting needed to make space for the change. Unlike a Bridgeport the bench mill generally doesn’t have enough table travel to get the job out of the way to make vertical room for the change. I very rapidly ran out of patience with winding the head on mine up and down via the short handle. A major reason why I built a bigger workshop and rolled a Bridgeport in as soon as I found an affordable one.

I would regard power driven rise and fall for the head on the big square column mills as essential. Not around when I got mine.

Concerning cutter holding I purchased an R8 ER collet set when I purchased my big square column mill. For some reason I pretty much never used it on the bench mill or on the Bridgeport I now drive. No rational idea why. I just don’t use it.

My go-to for ordinary jobs is a Posilok (Clarkson clone) collet chuck with both imperial and metric collets. Possibly not as good a choice now as it was 20 odd years ago as threaded shank cutters are less common but it does the deed for me. R8 collets and a set of Weldon Flat holders cover most of the odd stuff where a threaded cutter won’t do along with a some insert face mills on R8 shanks for bigger areas. Being adequately affluent retired old fart I can generally buy it if I need it. Unlike family guy (or gal) with other, more important, responsibilities who needs more care in choosing to get maximum bang per buck.

Were I starting over now I’d look very seriously at standardising on Weldon Flat style cutters for normal use and R8 collets for the outliers.  Get enough holders to keep one of each size and style permanently mounted then work CNC style swopping holder and cutter as a unit. You always know the stick out and, like the clarkson threaded cutter system, there are no pull-out issues. This would go well with a power drawbar. I imagine enough holders, say two of each size and the odd extra one where you use several cutters, would come out at around twice the price of an R8 ER set so not out of reach.

I’ve had a power drawbar set-up for my Bridgeport sitting in the cupboard for best part of a decade but never gotten round to fitting it. Mostly because the base fitting is for a belt shift speed change head rather than my vari-speed so I need to design a new adapter before I can use it but also because manual changing is generally not that much of an issue. Power would be nice, and quicker, but generally I mange well enough without. But sometimes …..

Clive

On 10 September 2024 at 21:08 grubscrew Said:

Just to elaborate, I was considering a power drawbar to facilitate tool changes, ie swapping between ER32 collet chuck, boring bar, drill chucks etc. I find it tedious removing the mills top cover, slackening the locknut, unscrewing the draw bar, tap to release the taper. Then the reverse after swapping the tool. If I’m lucky enough to spend a day in the workshop (rare), the time taken to swap tooling can add up.

Jason, I do have compressed air. I pondered using either a 3/8 drive ‘butterfly’ air tool or perhaps a battery powered 90 degree impact tool.

Having to remove the top cover to slacken a lock nut before you can deal with the drawbar is outrageously bad design. Totally intolerable and wants changing to a Bridgeport style sticking out the top with no locknut system. Which you will have to do anyway for a power drawbar.

Looked into the battery operated impact driver as a, maybe simpler, alternative to the air powered one around 4 or 5 years back. I found, and later lost, a Bridgeport reference suggesting that around 30 ft lb drawbar torque is needed to safely secure the drawbar on an R8 system.

As Bridgeport invented the R8 they should know.

Which is about what i naturally use with my spanner anyway. My 18 volt Makita 1/4″ hex drive impact driver struggles a bit but it will shift it after several uncomfortable seconds of rattling. The instructions have a graph running up to around 40 ft lb showing how long it should rattle for to loosen or tighten a given torque so it’s within specification. But sounds cruel. Up to 20 ft lb is comfortably quick to release. Beyond that I reckon is unreasonable for normal use. My Makita 1/2″ square drive impact wrench is way too powerful for that sort of job.

Clive

On 10 September 2024 at 22:16 Chris Mate Said:

The nearest I got to a power draw bar and threw away the time consuming  spanner, was to modify an old Singer knitting machine chiny handle with a socket, I just quickly put it on and swing the draw bar in or out of the MT4 in my case, and as others said long before you don’t have to overtighten it, and this handwheel just give me the right tighness with hand, I just remove it before starting milling.

Maybe R8 must be tightened well not to slip, not sure if its slotted.

R8 collets have a slot in the shank and a driving key in the mandrel (provided someone hasn’t mangled it by driving the machine too hard).  They don’t need huge tightening torque which is just as well as many machines don’t have a spindle lock.

It seems logical that the Bridgeport 30 ft lb recommendation applies to collets where enough force must be generated to securely hold the plain shank of a cutter.

For a drill chuck or similar separate holder on an R8 shank less torque will be needed to ensure its safe.

But R8 can slip and shear the key if insufficiently tight.

Be nice if there were some sort of reference giving the various slip forces involved when things are held by parallel grip or tapers, including interference fits. Preferably with clear nomograms so it’s fairly easy to see where various styles of holding fit in the grip range. Text saying what would be the icing on the cake. I’ve always disliked floundering around with specific recommendations for this and that with no clear connectivity.

Clive

Jason is quite correct in saying that the 14 V drill / driver I used for the Bridgeport drawbar tests maybe 10 years ago is, by modern standards, a bit weak. Still able to snap a 4 mm Screwfix gold screw if you lent on it too long tho’.

It was a Makita 8280D 14 V cordless percussion drill driver which I’d just retired from active service because I could get a new 14 V drill for less than two new batteries. Claimed to have a hard joint fastening torque of 36 Nm – 27 ft/lbit would go up to 40 ft/lb (ish) in impact mode so it seemed a good match for the Bridgeport draw bar. As I recall things it was pretty decent at tightening up when checked against a torque wrench but struggled when undoing. It really didn’t like undoing a hard joint it had tightened up to its maximum torque. As I couldn’t see any neat way of limiting the tightening torque to something it was happy to undo i abandoned plans to strip it and repurpose.

Seems to be pretty universal that drill/drivers and impact drivers are better at the tightening up business than the undoing one on hard joints. Never had one fail to shift in the odd emergencies when the proper tool was too far away but had to wait a while at times!

The modern breed are, of course, completely different animals.

My Makita DTD152 18V cordless impact driver will casually snap the head off a 5 mm Screwfix Goldscrew or LiDL 5 mm stainless wood screw given a moments carelessness, 2 or 3 rattles and its gone.

Looking at the instructions (cue chorus of Cheat!) the graphs show actual maximum tightening torque is 140 N/m – 103 ft/lb achieved after a bit over 2 seconds. At nominal 3,500 impacts per minute call it 120 beats. Enough to properly tighten an ordinary 16 mm bolt.

Way, way too much for the 7/16 UNF R8 drawbar thread.

Assuming the graph is accurate at the bottom end 30 ft/lb – 40 Nm translates to less than half a second, perhaps 30 impacts at most. Good luck with figuring out how to arrange that.

Best answer would probably be to find a drill whose stall torque is pretty good match to the required drawbar torque. Which is likely to be one of the smaller ones.

In drill mode my 18 V Makita DHP448 goes to 90 Nm – 66 ft/lb in low gear and 58 Nm – 43 ft/lb in high gear which looks promising. If stripped and the innards built into a suitable unit running off an external power supply it could be run on a lower voltage for tightening to 30 ft/lb (ish) and full voltage to undo so things should never jam. Not sure about speed tho’. Can’t see it hitting the book 2,000 rpm before things are tight or fully loose but still likely to be on the quick side for threads.

Smaller, lower voltage, one in low speed certainly seems a better bet.

Clive

Nice tool Jason. Bound to have rather more oomph than mine so I’d not risk it on a drawbar.

Assuming the Makita torque against time/number of impacts style graph is generic it’s pretty much certain to be way too tight at normal speed almost before you’ve realised it’s in impact mode.

But Makita don’t say anything specific about what happens if you use lower speeds. Just that it’s different. Odds are it’s very non-linear as the battery impact tools depend on fast light blows likely needing significant speed before anything much happens.

As I understand things good quality drawbars are heat treated for wear resistance and the ability to stand up to repetitive torsional stresses rather than thread strength. So the threads aren’t particularly strong. Presumably because, in extremis, it’s better to damage the thread on the drawbar rather than in the tooling.

Considering the 7/16 UNF thread on a Bridgeport drawbar typical maximum tightening torque quoted for Grade 5 (aka very ordinary) bolts is 65 Nm – 48 ft/lb. So the 30 odd ft/lb suggested by Bridgeport is comfortably under stressed for just about any steel.

After so many years I no longer recall why I didn’t take things further with my surplus to requirements 14 volt drill and play about with drive voltages to get a decent balance of tightening and loosening torque.

Most likely, as with so many of my stillborn “looks like a good idea” projects, due to the potential of too many devils in too many details.

The obvious one being mounting the thing. Typical battery drill with smooth plastic casing but no nice machined mounting collar like mains powered ones generally had. So I’d have had to make a new case for the innards with all the bearings in the right places et al.

Hand holding the thing just wasn’t going to fly unless I stood on a hop up or stool. A Bridgeport is tall! Dropping a ring spanner over the protruding drawbar hex is quite far enough up for me thank you.

My square column bench mill wasn’t seriously lower either as I had it set on a higher than usual bench for better visibility of work in progress without excessive bending over upsetting my back.

Maybe practical for folk with a more normal set up.

Even then best to plan on being comfortable reaching a foot, or more, higher than with a spanner if hand holding a battery drill or driver. Also the weight issue to consider as its close to working overhead. Which is always more tiring. Especially for old farts like me.

Clive