I respect your decision to try and cure your current account. I promise you it will take months to fix if not longer. Instagram limits exposure on every account. The more engagement your account receives, the more exposure that is granted by Instagram. Since your engagement is so low, Instagram is seriously capping your exposure in a negative manner.
I have learned this from my past mistakes. Instagram did not always consider engagement as the most important aspect to whether or not an account is granted more exposure. That being said, I would always buy 10k followers on new accounts I created so they get ranked faster and appear more popular. I continued to do this after the update (that limits exposure based on engagement) and the accounts that I did this to are growing so damn slow (still to this day). Back then I decided to create more accounts and I DID NOT buy any fake followers on them. To my supersize, these accounts had the same engagement rate within just a week, and the accounts grew 10x faster (or more).
In addition, I have also purchased Instagram accounts which appeared to have a good engagement rate. After i purchased the account, I noticed little to no new followers or likes. This was because the seller was just buying fake followers, likes, and comments on the account to make it look legit. The account is complete trash with 50k inactive followers and around 50 likes/picture.
I strongly recommend you consider the following proposal:
Continue to fix your current account. However create a new account as your backup plan also. Pop it on MassPlanner, and let it start growing on auto pilot by re-posting pictures from other accounts in the 3D printing niche. This way you are ahead of the game in case you choose to start fresh a few months from now.
Path #1 - You do not create a new account, and you spend a few months trying to fix the engagement on your main account. You then realize that its not working out, and you choose to start over by creating a new account. The new account has 0 followers, likes, comments, traffic, engagement. You will have some regrets that you did not start the new account sooner. You are not behind by a few more months.
Path #2 - You create a new account and set it on auto pilot. You continue to spend a few months trying to fix the engagement on your main account. You then realize that its not working out, and you choose to switch over to the new account instead. This new account has a around 10k followers by this time, and a decent engagement rate. You than thank @BrandonBerner for being so percipient, and looking out for your future of success.
Path #3 - You create a new account and set it on auto pilot. You continue to spend a few months trying to fix the engagement on your main account. HURAY! Your main accounts engagement is back to a healthy state. Now you have this new account that has a around 10k followers by this time, and a decent engagement rate. You can then choose to sell the account, or use it as a secondary source to generate more traffic to your main account in the forum of shoutouts, or you can add a link into the BIO to generate more sales.
My Stepdad always told me this saying through my child hood "Work Smarter NOT Harder". Although he may have used it for unnecessary things growing up, it has proved to be a very useful quote that I live by each and every day.