Frame Hole Drilling...

General Discussion about electric bicycles.
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Frame Hole Drilling...

Post by PlanetDad » May 22 2019 12:31am

Working on a plan to clean up my build and add some better mounting options.

Plan is to use some scrap galvanized sheet metal contractors left in the scrap bin at work, Bend and cut DIY style. Yes it will be "Custom" and not as clean as most, but that is kinda the point.

Question is: Will drilling 1/8th inch holes for riveting compromise the upper and lower tube?

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MTB Apperently 6061 Aluminum but its a Wally World donor
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Re: Frame Hole Drilling...

Post by flat tire » May 22 2019 1:47am

I think you're good to go.

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Re: Frame Hole Drilling...

Post by amberwolf » May 22 2019 2:00am

drilling may be ok, but if there is any frame flex at the point the hole is drilled, it may begin cracking at that point. it's not as big an issue with large diameter tubes as smaller ones, but I did eventually crack stays on the dayglo avenger, partly from the holes i drilled to rivet plates to it, for helping secure a cargo rack. i didn't have issues with the couple non-structural-load holes i drilled into the larger tubes.

but...it can happen.


if you intend to make an in-frame batteyr box, then i'd recommend instead making the whole box, then securing that inside the frame triangle, with clamps that go around the tubes for better lateral support, like if the bike fell over or you crashed, so it wouldn't rip the rivets out of the frame or the sheet metal, etc. there is a whole thread for home made battery housings, titled similarly, if you need ideas.

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Re: Frame Hole Drilling...

Post by ferret » May 22 2019 6:14am

It depends on the exact location of the holes.

It may be counterintuitive, but a small hole is more likely to start a crack than a bigger hole.

Have you considered using rivnuts? They're what some frames use to mount water bottle cages.

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Re: Frame Hole Drilling...

Post by wturber » May 22 2019 8:35am

Personally, I would avoid drilling holes if I could. I remember reading a report on the testing of a number of bicycle frames of different materials and failures tended to originate at welds and holes drilled in the frame. And those holes were factory made and presumably properly de-burred and finished. The components that usually failed were downtubes, chainstays and headtubes.
The photos of breakages with this article show that the cause of failure is often something small: drillings and steps should be avoided on the highly-stressed down tube, and on the chainstays. Small welds for components also are critical. Aluminum, especially, is sensitive to stress-risers, unforgiving of such “prior damage,” but titanium also is sensitive. It is indicative of the quality of the lightweight frames than none of them failed at a load-bearing welded or glued joint. Klein’s Quantum Race broke at the shift-cable entry hole in the down tube; Schmolke’s titanium frame, at a drilling for a bottle cage; Merlin’s Team Road, starting at the weld for a shift-lever boss. It follows that the dimensioning of the main tubes and their joints was appropriate.
A positive feature of steel frames went unexamined in this test: steel is not so sensitive to stress risers, and is more tolerant of minor damage. Also, surprisingly, steel frames have less of a problem with corrosion than many aluminum frames.
But if if I were to drill holes in a frame, I'd be sure to de-burr the holes inside and out. I'd avoid drilling downtubes and chainstays.
Seat tubes, seat stays and downtubes would be better candidates. And I'd be more likely to drill a steel frame than any other material. I grant that this is based on limited testing, but it seems better than just shooting from the hip.

https://www.sheldonbrown.com/rinard/fra ... e_test.htm
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Re: Frame Hole Drilling...

Post by donn » May 22 2019 10:52am

What they said. Plus, just guessing here, but some of the experience referenced above may be scenarios where the drilled frame member is subjected to approximately the same stresses as undrilled. A significant load added to the member, on top of the hole drilled in it, intuitively at least seems to be part of the problem here.

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Re: Frame Hole Drilling...

Post by docw009 » May 22 2019 11:05am

I'd not drill holes in an alloy frame either, although I did do it once to install water bottle mounts with tapped holes. I was advised to remove the taps and install rivnuts to relieve stress. Must be some magic from the clamping around the circumference of the hole.

I look at some commercial ebikes and thery have drilled holes for wires right next to where the frame welds into the stem tube. Does it mean ebike makers don't know what they're doing?

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Re: Frame Hole Drilling...

Post by fechter » May 22 2019 11:17am

It really depends on where the hole is located. Many parts of the frame will be primarily under compression where a hole won't tend to form a crack. In areas under tension, a hole is more likely to form cracks. The frame material matters too. Steel won't be much of an issue. Aluminum is more prone to cracks.

If you put some epoxy around the rivet, it should provide a significant percentage of the original strength.
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Re: Frame Hole Drilling...

Post by wturber » May 22 2019 1:38pm

fechter's point about compression vs. tension jibes with the destruction testing article. Downtubes and chainstays are generally in tension while the seatpost, top tube and seatstays are generally in compression.

One other thing not mentioned is whether the frame tubes are butted or not. Some tubes are thinner away from the weld/braze joints.

I'd also consider the kind of speeds and amount of use intended for this bike before deciding. The higher the stress and speed, the less I'd be inclined to drill. And if you do drill some holes, be sure to do routine inspections.
Last edited by wturber on May 22 2019 8:38pm, edited 1 time in total.
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Re: Frame Hole Drilling...

Post by Chalo » May 22 2019 1:47pm

docw009 wrote:
May 22 2019 11:05am
I look at some commercial ebikes and thery have drilled holes for wires right next to where the frame welds into the stem tube. Does it mean ebike makers don't know what they're doing?
From what I can tell, they really don't. Consider how often they use 12ga spokes with bicycle rims, and lace the spokes inside the flanges to further reduce an already miserably inadequate bracing angle. They often weld an unbraced, open-sided controller box to the bottom bracket shell, and then weld the chainstays to the box instead of to the BB shell. This is one of the highest stress points in a bicycle frame, and they completely screw it up.

E-bike manufacturers do usually have the good sense to make their frames extra heavy, which makes the frames slightly more fault tolerant.
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Re: Frame Hole Drilling...

Post by lionman » May 22 2019 8:59pm

My controller is currently cable tied under the down tube, not far above the bottom bracket.

I was considering installing some rivnuts/nutserts in the down tube to allow me to bolt the controller in place.

Is this a bad idea? Its a hydroformed alloy frame.

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Re: Frame Hole Drilling...

Post by docw009 » May 22 2019 9:18pm

Use brackets. These came from Home Depot plumbing department. Copper plated soft steel. I cleaned up the wiring later.
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Re: Frame Hole Drilling...

Post by PlanetDad » May 23 2019 1:35am

Wow, allot of good info to consider thank you! While researching this topic found some heated debates, and to me comes down to many different factor's, too much to consider much like battery life/range.

*Frame material and size of tube
*Suspension and pivot points
*Location
*Proper technique in drilling/cleaning bur's,
*Rivet vs. Blind rivet.

I'm confident enough to go forward. Going to follow some CAD stress maps for placement, although not correct frame design i'll have an idea on the least critical areas. Mainly because this is a road bike, biggest contenders are railroad tracks and poorly maintained roads. Of course watching the drill areas closely.

Didn't find much evidence of failure during my search. Anyone have experience with that?

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Re: Frame Hole Drilling...

Post by amberwolf » May 23 2019 1:51am

PlanetDad wrote:
May 23 2019 1:35am


Didn't find much evidence of failure during my search. Anyone have experience with that?
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Re: Frame Hole Drilling...

Post by lionman » May 23 2019 2:10am

docw009 wrote:
May 22 2019 9:18pm
Use brackets. These came from Home Depot plumbing department. Copper plated soft steel. I cleaned up the wiring later.
trek_ratter.jpg
Yeah I have considered those, but thought it may be difficult to find one that fits my down tube. If it was soft enough metal it wouldn't mater as could shape it accordingly, although my local hardware store only has steel saddle clamps that are big enough. Also, (I think) my down tube is tapered and is slightly narrower towards the bottom bracket, or at least it changes shape a bit, so there is a risk it would slip down over time, something it can potentially do now with just cable ties.

I have also considered getting some copper water pipe and just beating it into strips and making clamps a bit like yours too.

How did you get any decent amount of tension in the saddle clamps?

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Re: Frame Hole Drilling...

Post by wturber » May 23 2019 8:59am

docw009 wrote:
May 22 2019 9:18pm
Use brackets. ...
When I reinforced my seatpost mounted rear rack, I used these accessory light bar clamps brackets from Amazon. They are pretty beefy, moderately wide, made from aluminum and they have a rubber insert between the clamp and frame to reduce the chance that the clamp will dig in and nick the seat stay. Since the rack would be transfering a load, I placed these as close to the ends of the seat stays as practical.


There are a bunch of different clamps made for tubes that you can find on Amazon in addition to the hardware store stuff that docw009 mentioned.
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Re: Frame Hole Drilling...

Post by tolkaNo » May 23 2019 12:12pm

I'd recommend against it. Use stainless cable ties or 3d print brackets, do whatever you can to avoid it

If you do drill make sure you drill the smallest holes possible and deburr them to relieve stress

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Re: Frame Hole Drilling...

Post by markz » May 23 2019 1:31pm

I was going to post that friction drilling is a type of drilling that melts the metal and reinforces the hole on the outter side, with a rolled up bead of molten metal. I haven't seen it done on bicycles, and I'm not sure how old the technology is. But surely that strengthens the material around the hole.
https://youtu.be/FIgg6sey0C8?t=176

Can it be done on aluminum?
https://youtu.be/7rCN7Brj8cE?t=12

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Re: Frame Hole Drilling...

Post by markz » May 23 2019 1:50pm

I used normal rack mounts on dropout and they dont tend to last long with heavy loads. I am currently using a seat post rack, and will be putting together a stand for it. Another way to go is a seat post trailer mount, which I have used for a handlebar light for my Unibond, and hanging a 5S2P battery off that. That type of mount could be made out of angle iron with a tap set. I am currently using a method of drilling a hole in a hose clamp to put a mud guard rod through and attaching to fork. There are better quality hose clamps out there, T-bolt hose clamp. Using zip ties for certain applications is not ideal, unless you get high quality zip ties purchased anywhere but Home Depot, Lowes, PA/HF, C.T.->(EH) but places like Auckland Grainer, quality metal zip ties are good too. Example would be battery in triangle using duct tape then metal zip ties, too many times I had reg zips fail. Next that comes to mind, some have 3D printed a bottle cage mount, I havent seen one that uses both cage mounts using two cage (vert and angle tube).
- Bicycles with standard welded on racks.
- Bicycles with brazed on "welded" racks, MAP GAS + ROD + Nossle (HD, Lowes, HF/PA) could use same method to beef up holes drilled.

If you want to not mark up your frame, using pieces of rubber around the hose clamps/ties would save the paint.
Even duct tape.
https://youtu.be/pY7nx5Z6Kzo?t=216


wturber wrote:
May 23 2019 8:59am
When I reinforced my seatpost mounted rear rack, I used these accessory light bar clamps brackets from Amazon. They are pretty beefy, moderately wide, made from aluminum and they have a rubber insert between the clamp and frame to reduce the chance that the clamp will dig in and nick the seat stay. Since the rack would be transfering a load, I placed these as close to the ends of the seat stays as practical. There are a bunch of different clamps made for tubes that you can find on Amazon in addition to the hardware store stuff that docw009 mentioned.

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Re: Frame Hole Drilling...

Post by PlanetDad » May 23 2019 2:23pm

Avoiding mounting on the seat post/cargo rack. Tried at first when testing, too much weight in the rear. And I honestly find it a huge eye sore.

Condending with a down tube style battery, but not enough room to mount properly due to the rear suspension. (Limited time to wait for delivery, limited budget)

Looking like 4 holes in upper tube, and 2 in lower. Debur and adding some sort of, sealant or adhesive help?? Mainly to keep water out, maybe secure the drilling area?

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Re: Frame Hole Drilling...

Post by wturber » May 23 2019 5:26pm

markz wrote:
May 23 2019 1:31pm
I was going to post that friction drilling is a type of drilling that melts the metal and reinforces the hole on the outter side, with a rolled up bead of molten metal. I haven't seen it done on bicycles, and I'm not sure how old the technology is. But surely that strengthens the material around the hole.
https://youtu.be/FIgg6sey0C8?t=176
Or maybe it messes up the temper? I'd research further before assuming.
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Re: Frame Hole Drilling...

Post by flat tire » May 23 2019 6:17pm

Ignore all the naysayers. Check it for cracks frequently. Love to see something different, which riveted panels definitely is.

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Re: Frame Hole Drilling...

Post by fechter » May 23 2019 10:52pm

If the holes are in the sides of the tubes and not the top or bottom, the stresses there will be near zero so not much chance of cracking
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Re: Frame Hole Drilling...

Post by Chalo » May 23 2019 11:16pm

fechter wrote:
May 23 2019 10:52pm
If the holes are in the sides of the tubes and not the top or bottom, the stresses there will be near zero so not much chance of cracking
The forward and rear ends of the top and down tubes see rather large torsional loads. I had a sturdy big-tubed aluminum bike frame that cracked at the rivet holes that held the downtube cable guides. Those were OEM features from a very reputable and engineering-driven manufacturer.

The bright side is, if this modification scraps the frame, it's only a Wal-bike and the world is better off without it.
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Re: Frame Hole Drilling...

Post by markz » May 24 2019 4:08am

Good point!
wturber wrote:
May 23 2019 5:26pm
Or maybe it messes up the temper? I'd research further before assuming.

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