Reaming mild steel.

I tried reaming today. I was surprised by the rough looking finish I got on mild steel, it feels smooth but looks terrible.

Is this normal?

Do other metals come out similar?

Should look quite smooth, what size reamer and what size hole did you use? hand or machine?

J

15.7mm drill

then 16mm reamer in lathe at 99rpm. Soluble oil as lubricant.

I think the pilot hole is too big and the reamer is not working but rubbing some what

Hi Chris,

A sharp machine reamer is the best tool, use cutting oil, your speed was ok perhaps slightly slow 15.7 mm drilled hole is about right, slow feed in faster feed out.

Mild steel can give a crappy finish at the best of times.

Tony

You might want to think about adding another step to this operation.

If you drill then ream, it is possible the drill could have wandered out of true, the reamer will just follow the error.

If it is a critical hole I always drill the bulk out, then use a single point boring tool to take it out to reaming size then finally the reamer, that way it should end up concentric and true. You also have better control on how much to leave for the reamer to remove.

Phil

Speed and pilot hole are about right, although I use 15.8 pilot (depends what you have to hand, really) i.e. 0.1mm undersized up to 8mm, 0.2mm undersized above that. Lots of neat cutting oil lubricant. I can't say if the use of soluble oil will affect it, but I believe the neat oil is a better lubricant (rather than a coolant). Peck ream, removing chips frequently as the reamer descends quite slowly, in stages, withdrawing at each stage and brushing the chips off then lubricating. You should get a decent smooth finish. I did a 12mm hole yesterday and it looked good to me. What grade of 'mild' steel? EN1A or EN1A with added lead should both give good finishes (the leaded version being better). Maybe the odd scratch visible. EN3B (which is what I used yesterday) should also give a pretty decent finish but with a few more scratches visible.

What are the edges of the reamer teeth like, viewed under a loupe or a microscope?

Marcus

Leaving 0.3 on the bore is okay all the time the drilled hole is smooth, as the ruff surface finish could be what's left from the drilling operation. To achieve a smooth drilled hole double drill, that is, drill the pilot hole at 15mm and follow up with the 15.7, this will give you a size, smooth bore. Always use factory ground drills for this operation

Chris

I was taught that when reaming holes you use, half the speed and twice the feed, (of a drill) of course this is just rule of thumb. The other thing to remember a reamer is a sizing tool not a finishing tool, you can get a better finish with a drill. If it is finish you want then boring is the best option. The other thing is you have not said what type of reamer you are using, this can make a lot of difference.

Hi, I wasn't very clear, due to habit any hole I drill is the following:

5mm spot drill

4.76mm drill

7.84mm drill

12mm drill

for these 16mm holes I then use the 15.7mm drill.

Hand feeding a reamer will quite often give a poor looking finish, even though the bore may be accurate. Is a boring bar not an option? As mentioned it would give the best finish.

You haven't said which grade of MS your using, which could be the root of the problem, either that or a reamer that's seen better days

.

Chris,

As others have suggested; this is likely to be residual damage from the drilled hole.

Any tearing [in the drilled hole] that exceeds the diameter of the reamer will obviously remain after reaming; leaving pits in an otherwise smooth surface ... Which matches your description.

I would try a smaller and/or smoother drilled hole before blaming the reamer.

MichaelG.

Industrially reaming is a process used to produce lots of constant sized holes without stopping to gauge or measure each hole, or producing small deep holes which cannot be bored,the surface finish comes with experience and lots of it ,and during training if the engineering shop you worked in did not do much reaming then you did not learn much from older workers or like I did most of our reaming was in brass and very little steel,so I have always found reaming to be a bit hit and miss ,particularly on steel with holes above half inch diameter,good machine reamers will produce nice finishes in free cutting steels but can pick up on the rougher steels ie en 2 or 3 despite using lubricating oil,or soluble oil or modern Rocol type lubricants.Although not good practice and not good for reamer life boring or drilling the hole to only a couple of thou smaller and scraping the bore with the reamer can produce good finishes,why not bore to the required size ?,sometimes its safer to rely on the reamer to size the hole rather than risk boring to size,make a mistake and go oversize and spoil the work.The reamer also found a use when some companies running on worn out machines which would not bore true and measuring equipment was scarce, a reamed hole would be truer than what the machine could produce,Do not believe that our industrial past was built on factories with wonderful new machines, an awful lot had machines that were totally out of date or were worn out

warning on the second hand market there are a lot of reamers which have been ground undersize and not easily detected,

Hi All

For larger holes above about 7.5 mm adjustable reamers can make life a little easier. As long as you don't press them too hard. and you have a through hole, or a hole with room for the adjustment area at the bottom of he hole.

**LINK**

I notice that new ones from Asia are also fairly reasonable priced these days. They also pop up from time to time in auctions and garage sales, Sometimes in terrible condition, chipped blunt blades (Avoid) and sometimes very good. Over the years I have accumulated a set. The blades can be resharpened if you have a surface grinder. You can make your own simple jig.

They do have their idiosyncrasies.... They hate being turned backwards as it causes the swarf to be forced against the sides of the hole by the relief on the back of the cutting edges. Anyway that's a definite no go zone with any reamer, do it and you are likely to spoil the work and maybe jam the reamer tight.

They do not like heavy cuts, they are not as strong as a solid reamer and particularly in the smaller sizes. Push them too hard and they will break, I learnt the hard way. They are hand reamers not machine reamers although I guess you could use the bigger ones in a machine, My biggest is an inch and a half. I have not tried it.

As Mentioned by Nigel McBurney second hand reamers are often under size due to wear or resharpening. Or they are "specials" made for a particular job. Sometimes our own work is a little over or undersize also requiring a non standard size. The material being reamed and the sharpness of the reamer and the lubricant being used also has a significant effect on the final size of the hole. Even if using a properly ground to size solid reamer.

Adjustable reamers overcome these difficulties. The method I use is to measure the hole to be reamed and set the adjustable reamer to the same starting hole size and pass it through the hole, (Remember tuning clockwise only including when withdrawing). This should remove any high spots in the hole. once this pass is done I expand the reamer a small amount and repeat the process measuring the hole until it is at the required size.

If the hole is shallow in relation to depth the reamer must be kept straight, or you risk bell mouthing the hole.. screw on Pilots are available to assist in the larger sizes. Alternatively hold the reamer in a pillar tool or use the drill press or lathe tailstock to hold it straight (Turning by hand only)

This method is a lot slower than using one that is set to finished size, however by creeping up on the finished hole size I get accurate results and a good finish.

Regards
John

Edited By John McNamara on 14/07/2014 15:57:49

Another option may be to run an end mill down the hole, I find they leave a cleaner hole than a standard twist drill and may be accurate enough to use the hole as is. In this case a 5/8" end mill should make a hole slightly under size e.g. 15.875mm so that would leave only a small amount to remove with a reamer.

Bob