Reamer questions

[rezcar]

I may have missed the "general tooling" forum (since there's so many) but I am finding the need for reamers lately. In checking online, there's adjustable and non-adjustable.

One would think the adjustable ones would be more economical rather than having to buy a single reamer for every imaginable size. Thoughts? I plan to use them on metals as well as plastics.

Thanks!

[Geof]

Two comments:

Adjustable reamers do not have a very large range of adjustment so the really do not substitute for different sizes of reamers.

If you use a reamer on metal just once it is no longer suitable for use on plastics; for plastics reamers need to be absolutely sharp.

[christinandavid]

Even solid reamers are 'adjustable' in my opinion...

Don't bother with adjustable reamers if you don't want to live in constant fear that it will go bad...reamers are ground with an almost imperceptible taper to provide clearance at the back end whilst still providing support. When you alter an adjustable reamer that taper changes, and can result in inconsistent cutting.

DP

[rezcar]

Thanks guys.

DP, what do you mean solid reamers are adjustable also?

[christinandavid]

Hi, sorry to be so mysterious, I was refering to the arcane art of mutilating a reamer to get it to cut the size you desire.

These methods include: -
running a stone down the reamer to wear it down and make it cut small, running a stone over the leading edges of the flutes to burr it up and make it cut big,
chopping the end off to reduce the size by a fraction (utilising slight taper),
grinding an eccentric lead on a reamer to make it cut big,
running it at suicidal speed/no coolant to make it cut big.

All above techniques should be regarded as useful only in one-off situations, or for own tooling purposes, to recycle a reamer that may have otherwise outlived its usefulness. All of the above are essentially 'one-hole' solutions that will dramatically reduce the reamers ability to cut a consistent size.

From a production point of view (when you need reliability) the only acceptable modification is to grind the size down slightly using a cylindrical/universal grinder. You can probably take it down 0.1mm safely this way, any further will need to be done on a dedicated cutter grinder (and if that can't be done in-house, you may as well pay for the size you want).

Last place I worked had a plethora of 'odd' sized reamers, but with various combinations of hole-sizes/tolerances, it was surprising how many different jobs they could be used for.

Have never reamed plastic.

On metals would always give a brand-new reamer a quick stone to get it cutting the size printed on the shank straight away.

Always eyeball them to check they're running true.

Always run them slow if you need them to last.

DP

[rezcar]

Nice! That's what I thought you meant as I had read about doing that somewhere on the net.

Guess I will have to buy a set of one piece ones though, more money.

[christinandavid]

Depending on your needs you may be better off buying one-off 'quality' reamers as and when you need them, rather than a set of possibly 'inferior' reamers of standard sizes, some of which you may never use.

Either way, remember that their life span can be prolonged by chopping the end off as soon as cutting becomes erratic (you will see the wear on the corner of the lead-in chamfer. The lead-in must be reground extremely accurately though, and don't let the reamer get too hot in the process.

Be careful not to run too fast on plastics (some plastics can be quite abrasive). As well as running them slow, leave plenty of material for them to cut (5% of hole size minimum to size of lead-in chamfer maximum) to stop them rubbing and help them last. I used to leave lots in on titanium and would end up with looong bits of curly swarf rising up out of the holes. Great fun.

DP

[rezcar]

Thanks again for the detailed advice! Any recommendations on a quality manufacturer? I typically buy from Enco and try to buy the cheapest American made tool when possible.

[christinandavid]

Hi,

Guhring were always our tool of choice. Have looked on their site and they have a good 'tool navigator' feature - enter the details of what you are machining and it should come up with the optimum tool for the job.

You will see that material and flute form (straight or negative/positive rake) can be different depending on your needs. The bulk of my experience is with using HSCO (high cobalt content) reamers with the negative rake helix. Have only used the positive rake helix with the aforementioned titanium alloys (which is why the swarf rose UP out of the hole). It may be that this form is best for plastics, don't really know.

Have used carbide also, but also mainly on titanium. Have found carbide to be a bit problematic as it chips easier (don't drop it or leave it rolling around in a drawer) and it must also be running absolutely true to continue cutting reliably.

A HSS/HSCO tool is a bit more forgiving in this respect as it will flex as it enters the hole and true itself up - but only to a point! My technique therefore always involves piloting the first 1-2mm of the hole with a slot drill/endmill to about 0.05mm undersize. Have found that this helps true the reamer up and guide the reamer onto position until it reaches a depth at which it is supported.

Remember one part in particular which involved about 30 holes 4.5mm diameter through a 2mm wall thickness (nitriding steel). The guys were having problems reaming consistently. Most of the holes were tight and the odd one or two per part were massively oversize. To try to reduce this, they were circular pocketing the holes just undersize, then cleaning the part, using cutting oil, keeping part free of swarf, stoning the reamer etc. In the end they were reaming the part small and got someone else to ream them out later. Pointless eh? I changed the method slightly. Reduced the size of the pilot hole (left .5mm in). Circular pocketed the first .5mm of hole only. Slowed the reamer right down and let her fly with oodles of coolant. No more problems and the reamer lasted forever. Applied this to many more similar situations with similar success.

I don't get to do much reaming in my new role, and if I do its with an old battered thing that has already been much abused....sigh...




DP

[rezcar]

Thanks, I'm saving this page for future reference!

[Megahertz]

What does "stoning the reamer" mean? How do you do it? Why would you do it?

[christinandavid]

'Stoning' a reamer is a method employed by dodgy individuals who want their reamer to cut tight. It basically involves running the reamer and holding an oilstone up against the flutes to prematurely age them and reduce the o/d. This can work well up to a point, but the duller the reamer the more unpredictable the cutting action. A worn reamer will inevitably start to pick up and this will result in oversize/tapered/crap holes.

Running a stone down the leading edge of the flutes can achieve the opposite effect, but it must be noted that it tends to work best on reamers that have previously been 'stoned down'....these are generally toolroom tricks and shouldn't be considered on production work/critical parts!

DP