How to expand a gear hole

[ashare]

Hi All,

I need to expand a hole in the center of a gear made of plastic. I tried using a bench press and the gear's center got shifted. I believe that the material might have melted and caused this to happen and since the material is plastic I cannot firmly grip it. I have the same gear in brass. I don't want to take the risk of doing it again as it is expensive. Can anybody let me know what would be the best method to do it by retaining the center? Please note that my background is in the design of ICs and I hardly have any working knowledge of lathe and mills

Regards,
ashare

[dt2133]

Can you post pictures of the gear, and tell us what is the current and desired hole diameter.

[remauled]

use a round file and take your time

If the gear is made of plastic, you can use a reamer. Else a round file works well too. Just take your time and work in 1 direction, don't use excessive force and the file will bite evenly giving you a larger hole while maintaining the center.

[ashare]

Attached are the pictures of the gear. The pic in the gear is already 8mm dia with a shifted center. Gear hole by default is 5mm. I need 8mm. I don't mind changing to brass gear if I can get things done with more precision. <br> <br>

[dt2133]

You need to do this on a lathe or cnc machine. Can't do it manually, difficult to get accuracy you need.
Either some bros here have the lathe/cnc machine and want to help, or you can try SG Tooling at Fook Hai
see if Mike can help you (may be you can buy some tools from Mike).

[ashare]

Thank you for the suggestions. I am not too sure about the hand reamer technique. Mike is too busy I believe. I am a foreign student and it doesn't make sense to buy a lot of heavy tools in Singapore. Will check some other alternatives. Thanks again.

[dt2133]

I didn't mean to ask you to buy the heavy tools from Mike. I was hinting to you to buy something (not expensive but may be useful, something you can bring back home eventually) so that Mike cannot reject your request as you are his customer. If Mike want to help you, it is just a 5 minutes job. I am not sure if reamer tool can do the job. You want to note that reamer tool is a tapering tool, it is not meant to cut thick material. It will create a taper hole, and you need to file the hole further. You may want to use drill bits instead, but in a progressive manner. You start off with a 5.5mm drill bit, an then 6mm, and so on, until you reach 8mm. This might work.

[ashare]

I have bought tools from him but that doesn't entitle me for his support :-) I had tried the progressive drilling method only initially but it doesn't work. The plastic gear fails to self align with the drill bit. Would a step drill bit help if I use a brass gear? Something like 5,6,7,8. Since the first step of 5 goes in perfectly into the hole, and the other sizes should maintain center. Just a thought.

[Wongster]

Is the plaster soft? If I can grip it with my 3 or 4 jaw chuck without it deforming, I can help you expand the hole to 8mm.

Drop me a PM if you want. But if you have a lot, I may not be able to do it due to the lack of time.

Regards,
Wong

[mave]

I'm sure Mike wouldn't mind.. Right or not Mike

Anyway, your steps of the progressive sounds good. I would also probably do the following:

1) use the size of the drill bit that can have a nice fit into the gear, secure the drill bit into the bench press.
2)With the plastic still in the drill, adjust the vice and clamp the plastic. This should identify the center of the drilling.
3) (machine not started) move the drill bit up and down, make sure the drill bit does not push against the plastic but just fit into the hole snugly.
Alternatively, ask mike to demo his mini lathe machine with your plastic.
Good luck anyway.

I have bought tools from him but that doesn't entitle me for his support :-) I had tried the progressive drilling method only initially but it doesn't work. The plastic gear fails to self align with the drill bit. Would a step drill bit help if I use a brass gear? Something like 5,6,7,8. Since the first step of 5 goes in perfectly into the hole, and the other sizes should maintain center. Just a thought.

[ashare]

Thanks for the tip. The alternative method looks simpler though . Mike will have to demo it twice as I have two pieces to work with

[Wongster]

That's the way I would do if I'm lazy to employ the help of the DTI to centre a hole/bore under the spindle. But I would use steel dowel pin that has a nice fit to the bore. But if certain level of precision is required, no choice but to bring out the DTI.

Regards,
Wong

[ashare]

Thank you people, for all the suggestions provided. I finally got it done with good precision with the help of Wong, who took his time to carefully do it for me. Thanks a bunch, Wong. I really appreciate it.

Arish

[Wongster]

Pleasure. And nice meeting you.

Regards,
Wong