Drilling out weight plates and my new pro style dumbbells

[deiphid]

I had 144 standard weight plates, and 22 pro-style dumbbell handles. Problem? The handles are 28mm (approx. 1 1/16 inch), while many of the plates would only accommodate a 1 inch (approx. 25mm) bar.

I did quite a bit of online research to find the best way to deal with this issue, i.e. how to drill, bore, file or ream a 28mm hole in cast iron where there is already a 25mm hole. There are a few threads here on the equipment forum, but mostly just people asking for (and receiving) suggestions on how to do this.

Seeing as I have just successfully resolved this issue for myself, I thought I should share what I have learned from the experience.

1) Don’t do it. If there is an alternative where you do not need to do this, go with that option. I’ll get into how I found myself in this predicament later…

2) Making the best of a bad situation? I feel bad for you son.

Something to try first. If you’re making fixed dumbbells (as I was), get all your plates and handles in front of you, and try some different combinations. Some handles might have slightly smaller diameters; some plates might have larger holes.

I managed to get myself from a 144 plate problem to a 72 plate problem this way. Yay for manufacturing variances!

Just be wary that if there’s no slack in the hole, and the hole is not straight, the plate will sit on an angle on the handle… this can get pretty ugly, especially if you have a number of these skewed plates on the same dumbbell. I put the badly skewed plates to the side, and either drilled them, or used them as the end plate on the handle, as the shaft doesn’t have to fit all the way through.

3) Things still aren’t fitting? Best get yourself a drill press then. I basically got the cheapest one I could find. Looks like this:


4) Put your drill press on the slowest speed. Note, don’t put it on the fastest speed. You’re gonna want the belt on the smallest wheel on the motor side, and the largest wheel on the drill side.

5) Get a 28mm tungsten carbide tipped (TCT) hole saw – or get a bunch of them. Now, over the course of this exercise I purchased (and basically destroyed) a total of 5 of these puppies. I paid a range of prices for them.

What I actually found was that the US $8 bits from Ali Express worked just as well, or even better than the US $22 bits I purchased from a local tool distributor. I don’t doubt that the more expensive bits were probably better quality, and might do a better job of cutting tidy 28mm holes in stainless steel plate… but we’re not using them for that. The bits look like this:



6) Use cutting oil. It isn’t magic, but I think it helped prolong the life of the bits. Things were a bit less noisy (squeaky) as well.

7) I did cut some “plugs” out of wood with a slightly larger hole saw.

Basically the idea is that these fill the existing hole to make one continuous surface. The pilot bit of the TCT hole saw drills into the wood, and centres itself on the hole in the plug made when the plug was cut. I thought this was genius at first – but to be honest in the end I did away with the plug and the pilot bit entirely.

I found a new TCT bit (minus the pilot bit) would centre itself on the existing hole in the plate just fine. I clamped the plates sometimes, but most of the time I found the weight of the plates sufficient to stop them moving about.

8) These TCT bits will cut through a cast iron weight plate like butter at first. However, I found they were good for 15 plates, tops. There’s probably some ways of prolonging the life of the bit which I don’t know about. Other than using cutting oil, and going slow, I don’t have any tips. As soon as the bit starts cutting the cast iron it starts smoking, so I knew I was destroying the bit.

9) Full disclosure – there is probably a better way of doing this. Maybe a better drill press with a slower speed. Maybe it would be easier on a lathe.

10) Things I did try, and can confirm do not work as well:

- Hand drill and mini flap wheel – does ok at knocking the paint off, but if it was just a layer of paint in the way I suspect I would have been finished at step 2.

- Round file – not sure if it was my filing technique but I didn’t feel I got any purchase once I cut through the paint with the file.

- Dremel and grinding stone – this actually does work, but very slowly. Also I think I lost as much material off the stone as it removed from the iron.

- 28mm reduced shank HSS bit – fail. Expensive fail.

- 27mm and 29mm cobalt hole saws – the holes were actually already 27mm (or close), the 29mm bit cut through one plate, then kept sticking. I think this was a combination of the teeth dulling and the small diameter shank slipping in the chuck. Perhaps the reason the TCT bits worked was more to do with the torque the drill could transfer through the wide, hex shank.

- Grinding/filing the shaft of the handle. You’d think it’d be easier to fix 22 handles than 144 plates right? Might be so if you were to put the handles in a lathe and machine them down 1-2mm. I don’t have a lathe. I reckon doing this by hand was gonna take like 30 mins to an hour per handle… compared with one or two minutes per plate to drill them out. Plus the handles are chrome plated.

As for how I found myself in this predicament… well I wanted a set of pro-style dumbbells. These sorts of things aren’t easy to come by in New Zealand. I managed to source the handles from a local retailer (Elite Fitness). I would have liked straight handles, but they only had the ergo ezi-grip style – beggars can’t be choosers. I couldn’t find pancake style plates though. Elite’s standard plates all have annoying grip holes (even on 2.5kg plates!)

I was shopping for something else at Kmart and noticed they had standard 2.5kg weight plates with no grip holes. They’re about 3/4 inch wide, so good for pro styles. Not perfect, but a good option. I purchased one handle from Elite and one plate from Kmart to check the fit. The fit was good.

So I made an order for 21 more handles and 143 of the same plates.

The plates were not the same plates – at least 133 of them were not the same plates. I think the first plate I purchased (and 10 more like it from the store) were from an earlier batch. These plates fit well on the handles. The 133 additional plates which had to be ordered from the supplier were much rougher; they were actually quite poorly cast. Many of the holes were not straight.

Anyway, I had a bunch of plates and a bunch of handles, so I decided to make it work. I think knowing how much effort it was in hindsight, I probably should have returned the plates. Oh well, at least I’m really happy with the result.

Pro-style dumbbells, 5kg through to 30kg in 2.5kg increments:











I think the difference in weight plate quality/casting is quite evident in the last two photos.

[Synthetickiller]

Thanks for the write up!
I'm glad that you said that if there's a better way go that route. This will be useful to people in general.

[swimmer32]

I purchased a set of Ivanko DB's used a few years back, and then hit them with a wire wheel, cleaned them up, and repainted them. That was a decent project. I can't imagine trying to do what you did! They turned out pretty good - but I would have quickly called it a day.

[lsi1]

a reamer bit would probably have worked as well for this project but any way you go your probably going to go through a few bits unless you have a way to sharpen them.

[qaz123]

Surprised the standard drill bit didn't work since cast iron is pretty soft.

I've drilled out some plates but I had a decent sized drill press though.

[RemainDieHard]

Seems like a really odd choice to use a hole saw and plugs, vs a 1-1/16 regular drill bit. Must have been a quite tedious to center those, vs the regular bit would have self centered. Nice finished dumbbells though!

[deiphid]

Interesting comments on the regular or standard bit.

An engineer I spoke with was confident a 28mm reduced shank HSS spiral bit (like what RemainDieHard just posted) would easily do the trick. So I purchased one. It wasn't cheap - I spent more on that single bit than the five tct hole saws!

Maybe it comes down to the torque of the drill press, but the 28mm spiral bit barely made a dent in the plates.

I really did think it would be the best option, especially given the anticipated centering issues with hole saws.

But I actually found the hole saws centred themselves (of course I lined them up by sight as best I could before starting the press).

And when you think about it... the two HSS cutting edges of a spiral bit really shouldn't be as effective as the six TCT teeth of those hole saws. Considering the job at hand (removing less than 1mm from the outside edge of a hole)... a spiral bit is designed to cut from the centre out to the edge whereas a hole saw cuts just at the edge so I think it could be the more appropriate bit for the job?

A reamer would obviously be more appropriate, but they're an entirely new concept for me and I had no idea what I was buying.

[Cleveland33]

Seems like a really odd choice to use a hole saw and plugs, vs a 1-1/16 regular drill bit. Must have been a quite tedious to center those, vs the regular bit would have self centered. Nice finished dumbbells though!

If I remember this correctly, a standard twist drill only has two cutting surfaces vs what looks to be about 8 with the hole cutter he used.

Doesn't really apply here, but cutters are more efficient than twist drills because they cut less material - but since he is only removing 3mm and the cutter's cutting surface is likely that wide, it's moot.

I am guessing the best bet here (other than NOT doing it) would be an annular cutter over the hole cutter selected - they are more expensive, but this is exactly what they are designed for.

Edit to add: waiting for Stasher to give an actual expert opinion.

[Mechanon84]

Surprised the standard drill bit didn't work since cast iron is pretty soft.

I've drilled out some plates but I had a decent sized drill press though.

That depends on the composition of the cast iron, which varies wildly. For the most part is's actually pretty brittle and very difficult to tool.

[rlundregan]

Reps to Deiphid for taking on this experiment (science!).

We do get this question a lot by people who are usually clueless. We should probably provide a link to this thread in the future when this pops up.

[beefyron]

This should be a sticky, I thought of this years ago, I forget why. Maybe to get cheap standard 50-# plates converted to olympic.

[ampire]

This should be a sticky, I thought of this years ago, I forget why. Maybe to get cheap standard 50-# plates converted to olympic.

Not too many do this but it does come up from time to time. I don't know if its worth the hassle but I am glad the OP ended up with a decent result. Glad I can get pancakes here in the States as easily as ordering them off Walmart.